An optical modulation element unit is disclosed which employs a film-type optical function member and a reflective optical modulation element and allows dust prevention for the reflective optical modulation element while preventing an increased number of parts other than optically required parts. The optical modulation element unit includes a light-transmissive substrate, a film-type optical function member attached to the light-transmissive substrate, a reflective optical modulation element separately placed from the light-transmissive substrate, a cover member which surrounds a space between the light-transmissive substrate and the reflective optical modulation element, and a holding member which holds the light-transmissive substrate. The holding member has a guide portion which guides an air flow to a space along a surface of the light-transmissive substrate, the surface being a surface on the side opposite to the reflective optical modulation element.