An infrared sensor includes: a package; an infrared detecting element formed on the package, the infrared detecting element including a thermal detector and an absorber formed on the thermal detector which is configured to absorb infrared light rays of a specific wavelength that are detected by conversion of the infrared light rays into heat; and a cap formed on the package to cover the infrared detecting element, the cap including: a body having front and rear surfaces, through which the infrared light rays transmit; and a shielding film, with a window formed therein, provided on at least one of the front and rear surfaces of the body, the infrared light rays being reflected by the shielding film other than a portion of the shielding film having the window, and every one of the infrared light rays passing through the window of the cap impinging on the absorber.