An electric power conversion apparatus includes a channel case in which a cooling water channel is formed; a double side cooling semiconductor module that has an upper and lower arms series circuit of an inverter circuit; a capacitor module; a direct current connector; and an alternate current connector. The semiconductor module includes first and second heat dissipation metals whose outer surfaces are heat dissipation surfaces, the upper and lower arms series circuit is disposed tightly between the first heat dissipation metal and the second heat dissipation metal, and the semiconductor module further includes a direct current positive terminal, a direct current negative terminal, and an alternate current terminal which protrude to outside. The channel case is provided with the cooling water channel which extends from a cooling water inlet to a cooling water outlet, and a first opening which opens into the cooling water channel.