An electric power conversion apparatus, comprising: a channel case in which a cooling water channel is formed; a double side cooling semiconductor module that comprises an upper and lower arms series circuit of an inverter circuit; a capacitor module; a direct current connector; and an alternate current connector, wherein: the semiconductor module comprises a first and a second heat dissipation metals (522, 562) 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 comprises a direct current positive terminal (57, 394), a direct current negative terminal (58, 395), and an alternate current terminal which protrude to outside; and 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, characterized in that the semiconductor module is inserted into the cooling water channel through the first opening in a removable manner; the channel case is further provided with a second opening through which the capacitor module is placed; the first opening for the semiconductor module is disposed on both sides of the second opening for the capacitor module; and a plurality of the semiconductor module are arranged through the first opening provided on the both sides so that a long side of the first heat dissipation metal and the second heat dissipation metal of each of the semiconductor modules is set along a direction along which cooling water flows. a channel case in which a cooling water channel is formed; a double side cooling semiconductor module that comprises an upper and lower arms series circuit of an inverter circuit; a capacitor module; a direct current connector; and an alternate current connector, wherein: the semiconductor module comprises a first and a second heat dissipation metals (522, 562) 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 comprises a direct current positive terminal (57, 394), a direct current negative terminal (58, 395), and an alternate current terminal which protrude to outside; and 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, the semiconductor module comprises a first and a second heat dissipation metals (522, 562) 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 comprises a direct current positive terminal (57, 394), a direct current negative terminal (58, 395), and an alternate current terminal which protrude to outside; and 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, the semiconductor module is inserted into the cooling water channel through the first opening in a removable manner; the channel case is further provided with a second opening through which the capacitor module is placed; the first opening for the semiconductor module is disposed on both sides of the second opening for the capacitor module; and a plurality of the semiconductor module are arranged through the first opening provided on the both sides so that a long side of the first heat dissipation metal and the second heat dissipation metal of each of the semiconductor modules is set along a direction along which cooling water flows.