An imaging device unit includes: an imaging device having an imaging surface located on one side thereof in a width direction thereof and a rear surface located oppositely to the imaging surface; a heat radiating plate radiating heat generated in the imaging device, the heat radiating plate being arranged at the rear surface of the imaging device; and a signal processing substrate causing the imaging device to be operated. The heat radiating plate and the signal processing substrate are arranged opposedly to each other with a spacer being interposed therebetween and with a space portion being obtained therebetween.