An electric power converter 10 includes a flow passage FP1 formed so that cooling water can pass through while exchanging heat with semiconductor modules 51, another flow passage FP2 formed so that the cooling water can pass through while exchanging heat with a capacitor 52 and a reactor 53, and a plate-like connecting plate 200 attached in a state where a major surface thereof is disposed along a side wall 110 of a case 100. A groove 211 and a groove 221 that communicate between the flow passage FP1 and the flow passage FP2 are formed in the connecting plate 200.