The scandal - in which the data was faked for apartment buildings and hotels, leaving them vulnerable to even moderate tremors - outraged the public in the earthquake-prone country.
Hidetsugu Aneha, who has been stripped of his architect's license, appeared yesterday at the first hearing of his trial in the Tokyo District Court and pleaded guilty to fabricating data.
Aneha, 49, has previously admitted fabricating data for nearly 100 apartment buildings and hotels to cut costs for contractors out of fear that he would lose their business.
Many of the hotels have been forced to shut down, although some have reopened after reinforcement work.
Local governments have ordered residents of affected apartments to leave their homes and a few of the buildings are being torn down.
Aneha's wife was found dead in March, and media reports quoted police as saying it may have been suicide.