A sensor unit includes a metallic base member, a solid-state imaging element, and amplifier chips. The base member has a first placement surface and a second placement surface. The solid-state imaging element has a photodetecting surface, and is disposed on the first placement surface such that a rear surface and the first placement surface face each other. The amplifier chips are mounted on a substrate disposed on the second placement surface. The base member further has side wall portions facing side surfaces of the solid-state imaging element. The chips and the solid-state imaging element are electrically connected to one another via a bonding wire. The chips are thermally coupled to the base member via a thermal via of the substrate.