Officials in Isesaki City, Gunma Prefecture, north of Tokyo, say the owner of a runaway dog that attacked 12 people did not have his pet vaccinated against rabies as required by law.
The Shikoku dog escaped from its owner's home on Wednesday and bit nine children and three adults. The dog was later captured.
The officials say the owner neither registered his dog with municipal authorities nor had it annually vaccinated against rabies.
They also say the owner has seven Shikoku dogs, but only three of them are registered and records show that they were last vaccinated 10 years ago.
The city took an administrative action against the owner, who admits to having failed to fulfill his duties.
The police are investigating the case on suspicion of negligence resulting in injury and violation of the rabies prevention law.
The last human case of rabies in Japan was reported in 1956. The health ministry says there is no risk of getting the disease if people are bitten by a dog in the country.
But rabies remains a serious threat mainly in Africa and the rest of Asia. So dog owners in Japan have to register their pets at municipalities and get them vaccinated every year in case the virus is brought in from abroad.
Violators can be fined up to 200,000 yen, or about 1,340 dollars.
Meanwhile, police in Kanagawa Prefecture, neighboring Tokyo, are looking for another Shikoku dog that ran away on Thursday in Minamiashigara City.
The owner of the nine-year-old male dog says the canine slipped out of its collar during a walk. City officials say the one-meter-long dog has been vaccinated against rabies.