Abstract: A plate of a housing includes a plate layer including an inner surface defining a groove which extends in an extension direction, a cut surface directly extending from the groove, a first surface roughness of the cut surface, and a second surface roughness of the inner surface which is different from the first surface roughness. The plate layer is a remaining thickness of a preliminary plate cut to remove a thickness portion thereof, the groove is a portion of a recessed pattern of the preliminary plate which is defined by the thickness portion and the remaining thickness facing each other, and the cut surface which has the first surface roughness is an exposed surface of the remaining thickness of the preliminary plate cut along a direction intersecting the extension direction of the groove to remove the thickness portion of the preliminary plate.