An image sensor unit includes a light condenser that collects light from an object to be read, an image sensor that receives the light collected by the light condenser and outputs an image, and a housing that houses the light condenser and the image sensor. The housing includes a plurality of spacer attachment portions to which a first spacer that keeps a distance between the housing and a mount member can be detachably attached and for which distances between the housing and the mount member in a state where the attached first spacer abuts against the mount member differ from each other.