The new head of SoftBank Group's mobile unit, Miyakawa Junichi, is investing 20 billion yen, or about 180 million dollars, in his company's shares.
He says he wants to show his commitment to growth at the Japanese telecom giant.
Miyakawa took the reins as president and CEO on Thursday.
The mobile firm says it will lend him money to help buy the stock. Miyakawa is expected to own 0.3 percent of the company.