To provide a use management method and a processor for preventing user's unauthenticated use utilizing a licensing for another user by detecting the change of the user with the use of biometrics information and preventing leakage of biometrics information.

In an image processor 10 which collates an inputted discrimination code with a prestored discrimination code to perform authentication and executes image processing corresponding to an operation input when authentication is completed, a fingerprint read part 26 for reading fingerprint data (biometrics information), a RAM 14 storing fingerprint data read by the fingerprint read part 26 at operation input when the authentication is completed, and a control part 12 which collates read fingerprint data with fingerprint data stored in the RAM 14 when fingerprint data is read by the fingerprint read part 26 after storage of the fingerprint into the RAM 14 are used to detect the change of the user.