A power semiconductor module for an inverter circuit comprising: a case with a solid bottom and an opening formed therein; at least a first semiconductor element (155, 156) housed inside the case and held in place between a first DC conductor plate and a second AC conductor plate; at least a second semiconductor element (157, 158) housed inside the case and held in place between a second DC conductor plate and a first AC conductor plate; a positive bus bar electrically connected to the first DC conductor plate, through which, in operation, DC power is supplied; a negative bus bar electrically connected to the second DC conductor plate, through which, in operation, DC power is supplied; an AC bus bar electrically connected to the first AC conductor plate through which, in operation, AC power is supplied; a supplementary mold member that closes off the opening at the case; and a sealing resin member (350, 351, 333) that seals the semiconductor elements (155, 156, 157, 158), the conductor plates (315, 316, 318, 319) and is constituted of a material other than a material constituting the supplementary mold member, wherein, the positive bus bar, the AC bus bar and the negative bus bar extend from inside the case outside the case via the opening, the supplementary mold member comprises indentations, in which the positive bus bar, the negative bus bar and the AC bus bar are fitted such that the positive bus bar and the negative bus bar are disposed so as to face opposite and parallel to each other with a wiring insulating portion therebetween, the supplementary mold member comprises a plurality of resin leak-preventing projections formed so as to encircle the supplementary mold member and projecting out toward an inner surface of the power module case, and the sealing resin member (350, 351, 333) fills any space in the case left unoccupied by the supplementary mold member, the bus bars (315A, 319A, 320), the semiconductor elements (155, 156, 157, 158) and the conductor plates (315, 316, 318, 319). a case with a solid bottom and an opening formed therein; at least a first semiconductor element (155, 156) housed inside the case and held in place between a first DC conductor plate and a second AC conductor plate; at least a second semiconductor element (157, 158) housed inside the case and held in place between a second DC conductor plate and a first AC conductor plate; a positive bus bar electrically connected to the first DC conductor plate, through which, in operation, DC power is supplied; a negative bus bar electrically connected to the second DC conductor plate, through which, in operation, DC power is supplied; an AC bus bar electrically connected to the first AC conductor plate through which, in operation, AC power is supplied; a supplementary mold member that closes off the opening at the case; and a sealing resin member (350, 351, 333) that seals the semiconductor elements (155, 156, 157, 158), the conductor plates (315, 316, 318, 319) and is constituted of a material other than a material constituting the supplementary mold member, wherein, the positive bus bar, the AC bus bar and the negative bus bar extend from inside the case outside the case via the opening, the supplementary mold member comprises indentations, in which the positive bus bar, the negative bus bar and the AC bus bar are fitted such that the positive bus bar and the negative bus bar are disposed so as to face opposite and parallel to each other with a wiring insulating portion therebetween, the supplementary mold member comprises a plurality of resin leak-preventing projections formed so as to encircle the supplementary mold member and projecting out toward an inner surface of the power module case, and the sealing resin member (350, 351, 333) fills any space in the case left unoccupied by the supplementary mold member, the bus bars (315A, 319A, 320), the semiconductor elements (155, 156, 157, 158) and the conductor plates (315, 316, 318, 319).