A thermal detector includes a substrate, a support member, a spacer member, a thermal detection element, a detection circuit and a wiring part. The spacer member supports the support member over the substrate with a cavity part being formed therebetween. The thermal detection element is supported on the support member. The wiring part connects between the detection circuit and the thermal detection element, and has first through third conductive layer parts and a plurality of plugs. The first conductive layer part includes at least one layer disposed in the substrate. The second conductive layer part includes at least one layer disposed in the spacer member. The third conductive layer part includes at least one layer supported by the support member. The plugs respectively connect adjacent layers of the first conductive layer part, the second conductive layer part and the third conductive layer part, in a thickness direction of the substrate.