PURPOSE: To pecisely detect the side slip of a paper sheet for correcting the side slip even if the carried paper sheets are different in a kind.

CONSTITUTION: A reading means reads light passing through a paper sheet being in a carrying course at every plurality of lines, and a paper end detecting means 8 detects the end of the paper sheet from the above read data, and a detecting means 10 detects the side slipping quantity and its direction of the paper sheet on the data from the paper end detecting means 8, and a control means 12 controls a correction mechanism on the result of above detection for correcting the lateral slip of the paper sheet. In addition, a paper kind detecting means 13 detects the kind of the paper sheet, and a light quantity regulating means regulates the light quantity of a light source for making the light penetrate the paper sheet on the above detection.