PURPOSE: To improve the operation efficiency of an optical character reader and a processing speed at the time of high speed processing.

CONSTITUTION: An oblique line detecting roller part 3 preliminarily detects an oblique line for the tip part of a paper sheet 12 on a carrying path 7 and delivers the detected result to an oblique line correcting part 5 as preliminary data. The correcting part 5 calculates an oblique line correction value from the preliminary data, stores the calculated value as a preliminary correction value when it is included within a correctable range, and in the case of the outside of the range, outputs oblique line error information. The correcting part 5 calculates an oblique line correction value from leading picture data fetched by a picture input part 4 and compares the calculated result with the preliminary correction value. When a difference between both the correction values is included within a certain range, the correcting part 5 adopts the oblique line correction value and delivers the value to a character recognizing part 6, and when the difference is outside the range, adops the preliminary correction value to deliver the value to the character recognizing part 6.