Tokyo Electric Power Company says electricity supply will be fully restored to Chiba Prefecture from Friday onward.
The widespread power outage was caused by Typhoon Faxai, which made landfall in the Tokyo area early on Monday morning.
Some 410,000 households in Chiba Prefecture were still without electricity as of early Wednesday evening.
Kazuyuki Shiokawa of TEPCO Power Grid said in a news conference on Wednesday that the household number will likely be reduced to 400,000 by the end of the day.
He added that power will be restored to the Chiba City area on Thursday, and other areas will have electricity on Friday or later.
TEPCO had initially aimed at complete restoration of power on Wednesday. But the utility said the extent of typhoon damage was much more than it had expected.
Meanwhile, power was restored on Wednesday to the 1,300 or so households in Kanagawa Prefecture that had been without electricity.