PURPOSE: To provide the bill discriminating device which is suppressed to low cost and can be offered at a low price.

CONSTITUTION: This device has an MOS image sensor 1 or CCD image sensor which detects the optical pattern of a fed bill, an LED 10 which lights the bill, a conveyance speed detecting means 9 which detects the conveyance speed of the bill, a scan cycle arithmetic means 8 which calculates a subscanning time interval according to the conveyance speed of the bill so that subscanning density becomes constant, etc.; and the kind of money of the bill or the kind of money and whether the bill is genuine or not are decided by using the optical pattern detected by the image sensor 1.