A fixing device has a body case therein defining a housing chamber in which an object is housed and a cover that covers the housing chamber. The body case has one of a groove and a protrusion that engage with each other. The object has an other one of the groove and the protrusion. The groove includes a receiving portion and a positioning portion. The receiving portion extends in an inserting direction in which the object is inserted into the housing chamber. The positioning portion extends in an intersecting direction intersecting with the inserting direction. The cover has a restricting portion that is in contact with the object while the cover covers the housing chamber. The protrusion engages with the positioning portion when the object is fixed in the body case. The restricting portion restricts a displacement of the object in a direction opposite to the intersecting direction.