In a mirror unit, a first wall portion is higher than a second wall portion. A window member is disposed on a top surface of the first wall portion and a top surface of the second wall portion and is inclined with respect to a mirror surface. When any one of first to fourth wall portions is set as a first reference wall portion, in a cross-section perpendicular to the first reference wall portion, a first line passing through a first end at a side of the first reference wall portion in the mirror surface and a first corner portion formed at the side of the first reference wall portion by an outer surface and a first side surface in the window member intersects the first wall portion. A wiring portion includes a portion extending inside a base and leads outside a frame member.