To reduce the thickness and to expand the detection range of an optical sensor unit used in a paper sheet processing device. This paper sheet processing device (1) is equipped with: optical sensor units, each of said optical sensors having a light-emitting part (14) for emitting light to a paper sheet which is passing inside a conveyance path, a condensing optical system (11) for condensing the emitted light transmitting through the paper sheet passing inside the conveyance path, and a light-receiving part (15) for receiving the light which has been condensed by the condensing optical system (11); and a control means (30) for performing identification of a paper sheet to be identified on the basis of output signals from the light-receiving parts (15). This paper sheet processing device is characterized in that in terms of the intensity distribution of the emitted light in the width direction of the conveyance path, the intensity of each condensing unit (11) at the periphery of the optical axis center position is greater than the intensity of the condensing unit (11) at the optical axis center position.