A photographic lens system for forming an object image is placed in the lens barrel of an electronic camera. In a camera body, a beam splitter for forming branched optical paths and an image sensing element for photoelectrically converting the formed object image are arranged. An optical filter attached to a filter cap is inserted between the beam splitter and the image sensing element. The filter cap intimately contacts with the perimeter of the exit surface of the beam splitter and the perimeter of the image sensing surface of the image sensing element, thereby forming closed spaces, between the optical filter and the beam splitter and between the optical filter and the image sensing element, which allow incident light to pass through.