The invention provides a power conversion device. Miniaturization of the power conversion device is achieved and assembly of a sealing member is improved. The power converter includes a sealing member (80) in a loop shape sealing a space between a sealing surface (51a) of a cooler (59) and a sealing surface (25) of a casing (20). Either one of the sealing surface (51a) of the cooler and the sealing surface of the casing is provided with a groove (25a) in a loop shape enabling the sealing member to be fitted therein. A first positioning portion (25b) is provided on a bottom surface of the groove. The sealing member includes an internal sealing portion (81) with a circular cross-section and located along the bottom surface of the groove, an external sealing portion (82) with a circular cross-section and located so as to surround a looped outer circumference surface of the internal sealing portion, and a connected portion (83) that connects the internal sealing portion to the external sealing portion across an entire circumference of the loop. The connected portion includes a second positioning portion (85) capable of being fitted in the first positioning portion (25b).