A fixing unit includes a plurality of first engagement portions which respectively engage with a plurality of first to-be-engaged portions to restrict a movement of a heating unit in a third direction intersecting with a first direction and a second direction. A fixed unit includes a second engagement portion which engages with a second to-be-engaged portion to restrict a movement of the heating unit in the first direction. The fixing unit includes a movable unit, a supporting member, and a reciprocating mechanism. The supporting member supports the movable unit such that the movable unit is movable along the first direction. The reciprocating mechanism causes the movable unit to reciprocate. The reciprocating mechanism causes the movable unit to reciprocate once every time a plurality of sheets pass between a first rotation member and a second rotation member in the fixing unit.