Another subsidiary, Mitsubishi Shindoh, had manipulated data for metal products, Mitsubishi Materials said.
Mitsubishi Materials' subsidiaries falsified specification data before shipping some of its products to clients, the company said, adding that it is working with affected clients to ensure product safety.
Mitsubishi Materials said that inspection data was falsified on parts used in aircraft, automobiles and industrial machinery, with more than 250 customers potentially affected.
The company said that three of its subsidiaries faked data on products to meet specifications. Ltd., also supplied non-conforming products, although it has already confirmed with customers that they are safe, the company said, adding that its investigation has not so far uncovered any cases that raise the possibility of legal violations or safety issues.
A third unit, Mitsubishi Aluminum Co.
Mitsubishi Materials has a 45-percent share in a copper tube joint venture with Kobe Steel, including the Hatano plant that is at the center of Kobe's data-falsification scandal.
Similar troubles with faked or unauthorized inspections have tarnished the image of other major manufacturers such as Nissan Motor Co., Subaru Corp. and Kobe Steel.
On the main section on Friday, 1,329.64 million shares changed hands, dropping from Wednesday's volume of 1,603.39 million shares.
The Nikkei declined 0.4 percent to 22,428.83 in midmorning trade, after markets were closed for a national holiday on Thursday.
Takeuchi also said the company is carrying out a probe into all of its operations, including practices at its subsidiaries.
With affected Mitsubishi Materials products used in defence equipment including aircraft engines, Japan's defence ministry is working to establish the impact of the wrongdoing but does not now plan to stop using any equipment, Defence Minister Itsunori Onodera said on Friday. He said the ministry has asked related departments to investigate its causes and is seeking an explanation from Mitsubishi Cable on why it took so long to report the problem.
With affected Mitsubishi Materials products used in defence equipment including aircraft engines, Japan's defence ministry is working to establish the impact of the wrongdoing but does not now plan to stop using any equipment, Defence Minister Itsunori Onodera said on Friday.
Boeing Co is now looking into the issue, a company spokeswoman said.