An electric power conversion device is provided with a case (60) which includes: a first member (61) having a first region (73) defining therein a first passage (78, 79) in which a cooling medium flows, and a second region (74) disposed on a side of the first region; and a second member (88) disposed so as to at least partly overlap with the second region as seen from a direction orthogonal to the second region in a spaced apart relationship to the second region, and internally defining a second passage (91) connected to the first passage. A reactor (31) is positioned in the first region, and a switching device (33) is positioned on the surface of the second member facing away from the first member while a capacitor (35) is positioned between the second member and the second region of the first member.