An occupant monitoring apparatus includes: an imaging unit; an illumination unit; a casing in which the imaging unit and the illumination unit are installed; optical films provided on driver's sides of the imaging unit and the illumination unit and optically adjusting incident light; a cover covering the imaging unit, the illumination unit, the casing, and the optical films; windows provided in the cover so as to face the optical films; supports provided on window frame portions; and supports provided in the casing so as to face the window frame portions. The supports provided in the casing support end portions of the optical films from the windows side. The supports provided on the window frame portions support the end portions from an imaging unit side or an illumination unit side. The optical films are sandwiched in the thickness direction.