Japan's Mizuho bank is blaming a malfunction in its core computer system for a service disruption on Wednesday.
The outage is the latest of several this year involving the system.
Sources say Wednesday's failure knocked out about 100 automatic teller machines and internet-banking services.
They say services were quickly restored after a backup system kicked in.
The megabank suffered breakdowns in February and March in the system that manages deposits, remittances and other key operations.
System trouble also halted over-the-counter transactions nationwide on August 20.
Mizuho says it is conducting a thorough check to prevent a recurrence.
The series of glitches have prompted the Financial Services Agency to launch a probe.