Mirror unit

A mirror unit comprising:

• a base including a main surface and a rear surface opposite to the main surface,
• an optical scanning device including a movable portion and a mirror surface provided on the movable portion, the optical scanning device being disposed on a side of the main surface with respect to the base,
• a frame member disposed on the side of the main surface with respect to the base so as to surround the mirror surface when viewed from a first direction;
• and
• a window member attached to the frame member so as to cover an opening of the frame member,
• wherein the frame member includes a first wall portion and a second wall portion which face each other in a second direction perpendicular to the first direction,
• wherein the window member is disposed on top surfaces of the first wall portion and the second wall portion,
• wherein the main surface is provided with a depression,
• wherein at least part of the movable portion of the optical scanning device faces a bottom surface of the depression,
• wherein in a cross-section passing through the mirror surface and parallel to both the first direction and the second direction, at least one of a thickness of the first wall portion and a thickness of the second wall portion in the second direction, and also a thickness of the window member, are greater than a distance from a disposing surface of the base on which the optical scanning device is disposed to the bottom surface of the depression in the first direction,
• wherein a height of the first wall portion from the main surface of the base is greater than a height of the second wall portion from the main surface of the base, and
• wherein in the cross-section passing through the mirror surface and parallel to both the first direction and the second direction, a corner formed by an inner surface and a side surface of the window member, the side surface being on a side of the second wall portion, is on a side of the optical scanning device in the second direction relative to a corner formed by a top surface and an outer side surface of the second wall portion, the outer side surface being a surface opposite to the optical scanning device in the second direction.