Sumitomo Mitsui Banking Corp. said Monday its automated teller machine systems in eastern Japan failed during the morning for a short period.
The ATM systems were restored around 9:50 a.m., the company said.
The Financial Services Agency will ask the bank to submit a report outlining the trouble, based on guidelines under the banking law, FSA Commissioner Shokichi Takagi said.
"We were informed that there was a problem with the hardware of the communications equipment, and we are investigating the cause," Takagi said. "We will ask for further information and urge the bank to prevent a recurrence."
The disruption affected some 1,500 ATMs in eastern Japan, an SMBC spokesman said.
Bank officials said malfunctioning telecommunications equipment at a computer center housing the bank's main trunk computer system appears to have caused the paralysis.
The bank, created April 1, 2001, through the merger of Sumitomo Bank and Sakura Bank, has about 7,500 ATMs, including machines at convenience stores, across Japan.
It has gradually been integrating the ATM systems of its two predecessors since April. The system failures are believed to be unrelated to the integration procedures, however, as no such work has been carried out recently, it said.