A power circuit section is adhered to a circuit arrangement surface on a heat
radiation
member to form a circuit assembly. A casing body is mounted on the heat radiation
member. The casing body is provided with an opening that exposes at least the upper
portion of the power circuit section. A shape retention member is disposed across
the opening for interconnecting a peripheral edge of the opening to each other
at a plurality of positions. A casing unit is made of a synthetic resin. The shape
retention member suppresses a deformation of the casing body due to a shrinkage
cavity. After cooling the casing unit, the shape retention member is removed to
define a large opening, if desired.
