PURPOSE: To enable a film to be detected in its residual amount with no damage given to the film further with no bad influence given to the action of winding and rewinding by providing a detecting means which detects a beam of light reflected at an angle in accordance with a winding diameter of the film.

CONSTITUTION: A laser beam generator 10 is set up in a position irradiating a beam L of light from a predetermined direction to the peripheral surface of a film F, while a CCD sensor 20 is opposed to the peripheral surface of the film F and set up in such a manner as to enable a reflected beam of the beam L of light to be detected by any of the elements. A signal in accordance with a winding diameter of the film is output from the CCD sensor 10. A control circuit 23 feeds a display data signal DS, corresponding to the time till the maximum peak of an output CCS of the CCD sensor 20 is generated, to a display circuit 24. Accordingly, applying no force directly to the microfilm F, its residual amount can be detected.