Investigators from the Tokyo District Public Prosecutors Office searched the offices of Lower House member Akimoto Masatoshi on Friday.
They suspect he received tens of millions of yen, or hundreds of thousands of dollars, from Japan Wind Development.
Sources say the firm is suspected of bribing the side of Akimoto over offshore wind power generation. The government is promoting renewable energy to help realize a carbon-neutral society.
Japan Wind Development purportedly failed to join an offshore wind power generation project, for which the government held bidding between 2020 and 2021.
Akimoto took up the bidding process during a Diet session in February of last year, asking that evaluation standards be reviewed from the next round.
The legislator served as Parliamentary Vice Minister of Infrastructure from August 2017 to October 2018. During the tenure, he was involved in drafting a bill to facilitate the introduction of offshore wind power generation.
On Friday, Akimoto resigned as Parliamentary Vice Foreign Minister, a position he had held since August of last year.
The prosecutors are believed to be investigating the opaque flow of money and what connections, if any, the company has had with the lawmaker.
Japan Wind Development told NHK that some items of objective evidence prove the firm has never bribed Diet lawmakers or any other public servants.
The company's website says Japan Wind Development was founded in 1999 and is engaged in the development and sales of wind-generated electricity.
The website says the company has 293 wind power generation units in and outside Japan for a combined output of more than 570 megawatts. It also says the firm is operating onshore wind power generation plants at 34 locations across the country.
Government pushes offshore wind power generation
The Japanese government regards offshore wind power generation as a trump card for making renewable energy the country's main source of electricity. It aims to expand Japan's power generation capacity to over 30 million kilowatts by 2040. That's equivalent to more than 30 large thermal power plants.
But Japan lags behind other developed countries, such as those in Europe.
The Japanese government legislated a law to promote offshore wind power in April 2019.
Under the law, the government designates sea areas for offshore wind power generation and entrusts operators picked through public tenders to engage in power generation in those areas for up to 30 years.
The government solicited tenders for three projects off Akita and Chiba between 2020 and 2021. In December 2021, a consortium led by major trading house Mitsubishi Corporation won all the bids by offering by far the lowest prices.
In October 2022, the government revised its assessment criteria for selecting operators, citing the need to help foster the industry by encouraging diverse entities to enter the business.
The new criteria put more emphasis on the speedy implementation of a project. They also impose a cap on the size of the power output to be generated by a single group of bidders.
The guidelines also require that if bidders propose tender prices that are less than certain amounts, they should be regarded as the same amount, and that assessments should focus not just on prices but on overall proposals.
In December last year, the government started inviting bids for four offshore projects based on the revised guidelines. The tender was closed in June.
Akimoto has been promoting renewable energy
Akimoto Masatoshi has been a vocal advocate for the promotion of renewable energy in Japan. He serves as a leading figure in the LDP's parliamentary group that supports such energy.
Akimoto often asked questions in the Diet about the advancement of offshore wind power generation.
At a subcommittee meeting of the Lower House Budget Committee in February last year, he called on the government to review the evaluation criteria for bidding from the public offering for the next offshore wind power project and focus on the speed of setting up operations.
He insisted that the government evaluate companies that are eager to start operations early.
Then Minister of Industry Hagiuda Koichi responded that changing the criteria would be difficult as the government had already started the bidding process several months earlier for one of the projects.
But Akimoto repeatedly asked for a review of the evaluation criteria, saying it was a political decision.
Unlike the then minister's response in the Diet, the government temporarily suspended inviting bids for the project the following month. In October last year, the government implemented new bidding standards, such as focusing on the early start of a project.
Hagiuda's successor, and current Industry Minister Nishimura Yasutoshi spoke to reporters on Friday.
He admitted that the ministry received proposals from a parliamentary group promoting renewable energy where Akimoto serves as the secretary general. But he says the review of the standards was appropriate. Nishimura said, "The review process was decided after discussions at a council including outside experts as well as a public comment."