The problems first surfaced late on Monday, when a flood of money transfer orders inundated some branches, the bank said. That led to problems in the bank's overnight payment processing system and affected services on Tuesday.
The system never managed to recover.
On Thursday, the bank's nationwide ATM network of more than 5,600 machines was forced offline from 9am until midday, then it failed again in the evening.
The ATM network had more problems on Friday, and the bank said it was unable to process regular salary payments worth ¥120 billion (US$1.5 billion) into the accounts of up to 620,000 people.
The bank currently has a backlog of more than 1 million unprocessed payments worth around ¥700 billion, it said Friday morning.
It hopes to clear that backlog and return system stability by suspending ATM and online services over the weekend. The bank will open branches over the three days and allow account holders to withdraw up to ¥100,000 in cash at bank counters.
The glitch, while not directly connected to last week's massive earthquake and tsunami, comes as Japan is dealing with the outcome of that disaster, an emergency at a nuclear power plant, and disruption to transport and other services caused by power blackouts.
