A rear-surface-irradiation-type infrared sensor includes a substrate having a through hole passing through between an upper surface and a lower surface; an infrared absorption part on the substrate on a side of the upper surface separate from the substrate by the through hole; and a temperature sensor part detecting a change in a temperature of the infrared absorption part. The through hole includes a first through hole part having an opening on the upper surface and one or more second through hole parts having shapes different from the first through hole constituent part. The first through hole part and the second through hole part(s) communicate with each other. In a cross-sectional shape of the through hole on a plane perpendicular to the upper surface, an inside wall of the first through hole part is outside an inside wall of the of second through hole part(s).