To authenticate a signature by comparing it with a preliminarily stored reference pattern for securely authenticating the signature and enhancing security.

The motion of a pen is detected by a motion detection part 1. The degree of similarity between the motion pattern of the pen detected by the motion detection part 1 and the motion pattern stored in a reference pattern storage part 31 is detected by comparing the motion pattern of the pen detected by the motion detection part 1 with the motion pattern of the pen by the signature preliminarily stored in the reference pattern storage part 31 by a comparison part 23. The result detected by the comparison part 23 is displayed on a display part 5.