Image sensor unit, paper sheet distinguishing apparatus, reading apparatus, and image forming apparatus

An image sensor unit that reads a reading target object by receiving light from the reading target object, comprising:

• a lens array that condenses light from the reading target object;
• an image sensor that receives the light condensed by the lens array;
• an elongated housing elongated in a first direction and that supports the lens array and the image sensor, the elongated housing having a side surface extending in the first direction;
• and
• an elongated rigid member that has a facing surface facing the side surface and an opposite surface opposite to the facing surface across a thickness of the elongated rigid member,
• wherein
• the elongated rigid member is provided with a penetration-hole that extends from the facing surface to the opposite surface, and the opposite surface of the elongated rigid member has a protrusion,
• a protrusion provided on the side surface extends through the penetration-hole, and
• the protrusion on the opposite surface of the rigid member extends into the protrusion on the side surface that extends through the penetration-hole.