Mirror unit and optical module

A mirror unit comprising:

• a mirror device that includes a base including a first surface and a second surface opposite to the first surface, and a movable mirror supported in the base to be movable along a first direction that intersects the first surface;
• an optical function member including a third surface that faces the second surface, and a fourth surface opposite to the third surface;
• and
• a fixed mirror that is disposed on a side opposite to the mirror device with respect to the optical function member,
• wherein the mirror device is provided with a first light passage portion that constitutes a first portion of an optical path between a beam splitter unit that constitutes an interference optical system in combination with the movable mirror and the fixed mirror, and the fixed mirror,
• the optical function member is provided with a second light passage portion that constitutes a second portion of the optical path between the beam splitter unit and the fixed mirror, and
• the second surface of the base and the third surface of the optical function member are joined to each other.