An image sensor unit includes: a plurality of light sources each including an LED chip; a plurality of light guides that are arranged in parallel to face incident surfaces on one side in a longitudinal direction for each of the plurality of light sources and that guide light from the plurality of light sources to a bill; an image sensor that converts light from the bill to an electric signal; a sensor substrate for mounting the image sensor; and a circuit board that is provided with the plurality of light sources on a same mounting surface and that is arranged on the sensor substrate on one side in the longitudinal direction of the plurality of light guides, wherein the sensor substrate includes a connection hole on one side in the longitudinal direction of the sensor substrate, and the circuit board is connected to the sensor substrate by connecting a connecting portion including a plurality of external connection pads to the connection hole.