A sensor unit 2A includes a metallic base member 20A, a solid-state imaging element 30, and amplifier chips 40. The base member 20A has a first placement surface 21 a and a second placement surface 21b. The solid-state imaging element 30 has a photodetecting surface 32, and is disposed on the first placement surface 21 a such that a rear surface 33 and the first placement surface 21a face each other. The amplifier chips 40 are mounted on a substrate 50 disposed on the second placement surface 21 b. The base member 20A further has side wall portions 25 facing side surfaces of the solid-state imaging element 30. The chips 40 and the solid-state imaging element 30 are electrically connected to one another via a bonding wire 92. The chips 40 are thermally coupled to the base member 20A via a thermal via 53 of the substrate 50.