A thermal detector includes a substrate, a thermal detection element and a support member. The substrate has a recess part with a bottom surface of the recess part being a curved light-reflecting surface. The thermal detection element has a light-absorbing film. The support member supports the thermal detection element. The substrate and the support member are arranged to form a hollow part therebetween. The support member includes a light-absorbing part in which impurities are dispersed in polycrystalline silicon with the light-absorbing part being arranged in at least a part of a surface of the support member facing toward the hollow part so that the light-absorbing part being irradiated by light.