The data is a reminder that the economy in the world's third-biggest power generator is in its sharpest contraction since the oil crisis in 1974.
Japan's industrial production fell 10.2 percent in January from a month earlier, the biggest fall on record, revised government data showed. The February data is due out later this month.
The 10 utilities generated 74.47 billion kilowatt-hours of electricity in February, marking the seventh straight monthly decline, the Federation of Electric Power Companies of Japan said. It was the first time since February 1997 that all the firms had reported falls in electricity generation.
"It's shocking. I didn't think (the fall) would top 10 percent," said an energy analyst at a Japanese brokerage, who spoke on condition of anonymity.
He said power generation normally rises or falls in line with real gross domestic product data, excluding the temperature factor.
Japan's economy shrank 3.2 percent in the final three months of last year, revised government data showed.
Japan's weather, which has been milder than normal since late January, is projected to stay mostly warmer in the coming month, the meteorological agency said.
Thermal power output plunged 29.6 percent, the biggest ever drop, helped by a rise in the nuclear utilisation rate of 10.8 percentage points, to 67 percent. That helped more than halve the utilities' consumption of oil, the most expensive fuel in the energy mix.
Fuel burn will decline further if Tokyo Electric (TEPCO) is allowed to restart the world's largest nuclear power plant for the first time since it was closed by a major earthquake in July 2007.
TEPCO's plans to restart the No.7 generator at the Kashiwazaki-Kariwa nuclear plant suffered a setback after a local governor said he would not grant approval for a restart until the company issues satisfactory plans on how to prevent outbreaks of fire there.
The analyst who spoke on condition of anonymity projected the No.7 unit would be restarted in the business year starting on April 1.
Industry researcher Japan Electric Power Survey Committee projected last week that demand from the the industrial sector, which started falling in October due to the economic slowdown, is unlikely to turn positive until February or March 2010.