The infrastructure ministry plans to question a Toyo Tire & Rubber Co. official suspected of falsifying performance data for its quake-absorbing equipment as soon as next week, ministry sources said.

The Land, Infrastructure, Transport and Tourism Ministry aims to clarify what led to the data falsification, the sources said Friday.

Toyo Tire & Rubber has said the official in charge of product development manipulated performance data due to pressure to meet delivery deadlines.

The ministry said Friday it has asked 26 companies that produce similar products, including Bridgestone Corp., to report by April 20 if there have been any cases of improper acquisition of product certification or if there are any substandard products.

Subject to the examination are 167 types of products that have been certified since 2000.

The ministry asked the 26 companies to check internal data and question the appropriate employees.

"The certification system assumes that performance experiment data are correct," said infrastructure minister Akihiro Ota.

So far, 55 buildings including condominiums, hospitals and local government offices in 18 of the 47 prefectures have been found using the substandard quake-absorbing equipment produced by Toyo Tire.