The initial inspection was held to check a wide range of facilities at the plant's No. 2 reactor after the great earthquake that hit northeastern Japan. The operator is hoping to restart the reactor about 100 kilometers north of the crippled Fukushima Daiichi plant.
But Japan's Nuclear Regulation Authority pointed out last year that Tohoku Electric's inspection was lax and the firm was re-examining the inspection records on the No. 2 reactor.
Company officials said at a news conference on Wednesday that the utility has scrutinized all the inspection records for the reactor since August 2011.
They said in some cases workers entered "no problem" for parts that didn't exist, citing the example of monitoring equipment for a valve which was not there.
In other cases, incorrect product types and serial numbers were left untouched. They say there were 4,188 errors in total.
Managing Director Takao Watanabe apologized to people in the region for causing concern, although he asserted the improper entries will not lead to any safety problems.
The company says it will also check the inspection records for the No.1 and No. 3 reactors.