An image sensor unit performs image reading by reflected light and image reading by transmitted light with respect to a bill, and includes a reflection reading light guide that emits light from a reflection reading light source toward the bill, a transmission reading light guide that emits light from a transmission reading light source toward the bill, an imaging element that focuses light from the bill, and a light receiving element that receives light that is collected by the imaging element. The transmission reading light source and the transmission reading light guide are disposed on the opposite side of a conveyance path through which the bill can pass, for the reflection reading light source and the reflection reading light guide, and a light blocking member that blocks a part of the light from the reflection reading light guide is disposed between the reflection reading light guide and the transmission reading light guide.