To detect remaining amount of a sheet-like medium by using a light emitting means and a light receiving means at low cost with high precision.

Light in a light emitting part 100 is received by a light receiving part 101 by penetrating a bundle of sheet-like media (first quantity of light). Next, in a control part 110, the sheet-like medium is fed by a paper feeding part 31, and light in the light emitting part 100 penetrates a bundle of sheet-like media constituted by the reduced number of sheet-like media and is received by the light receiving part 101 (second quantity of light). A computing part 111 obtains amount of increase by using the first quantity of light and the second quantity of light to detect remaining amount of sheet-like media by computing and processing by using an expression of circumference.