Almost 80 percent of Japan's banks store personal data on at least 100,000 people each, a Cabinet Office survey showed Monday.
The figure tops 50 percent in the retail and tourism sectors as well, at 62.6 percent and 55.0 percent, respectively.
The government conducted the survey on 10,000 major companies in February. Only 2,974 responded.
"The more information a company possesses, the greater the responsibility it bears should that information leak," a Cabinet Office official said, stressing the need for proper information management.
A set of laws governing the protection of personal data entered force April 1.
According to the survey, possession of personal data was highest in the financial sector, where 78.3 percent of the banks that responded they kept data on at least 100,000 customers.
Construction and wholesale companies, however, were far less likely to store personal information, with figures of 6.9 percent and 19.3 percent, respectively.
Meanwhile, 46.5 percent of Internet service providers said they kept personal data on at least 100,000 people. Insurance companies came in at 52.3 percent.
The information protection laws aim to safeguard the use of such data as names, addresses, birth dates, details of physical appearance, personal assets and job descriptions.