PURPOSE: To provide a device which is excellent in medium handling by eliminating the limit of the thickness of media handled by the device.

CONSTITUTION: In a double medium running detecting mechanism to detect the double running of media by detecting the difference between each quantity of the light transmitted into a light transmission type optical sensor with the light transmission type optical sensor arranged on the passage on which media run, information 12 is recorded by kinds beforehand, by which the type of information can be distinguished, and a reading means 14 is provided to read out the information 12, and a double medium running judging data table 16 by types is provided to call the medium double running judging data corresponding to the type of the medium handled from the double medium running judging data table 16 to judge medium double running.