An electric power converter, comprising: - an inverter which comprises plural electric parts; - a smoothing capacitor configured to smooth electric power; - a first conductor portion configured to connect the smoothing capacitor and the inverter, and - a housing configured to house the inverter, the smoothing capacitor and the first conductor portion; wherein: - the housing comprises a base portion having a mount surface on which the inverter and the smoothing capacitor are mounted, - the base portion is made of an insulating resin material, - the housing comprises a cover portion made of metal material attached to the base portion to cover the inverter, the smoothing capacitor and the first conductor portion, and - the housing comprises a metal thin plate formed on a lower surface of the base portion opposite the mount surface, - the metal thin plate is larger than an outer shape of the lower surface of the base portion and functions as a bottom plate of the cover portion, - a stepped portion having an end surface abutted with the mount surface of the base portion is formed in an inside part of the side wall of the cover portion and a leading end surface of the side wall is abutted with an outer peripheral edge of the thin plate, - the first conductor portion is placed in the vicinity of or in contact with the mount surface of the base portion of the housing in the middle of connection between the smoothing capacitor and the inverter, and - the base portion comprises a first coolant flow passage through which a coolant that cools the inverter can flow which is formed below a part where the inverter is mounted. - an inverter which comprises plural electric parts; - a smoothing capacitor configured to smooth electric power; - a first conductor portion configured to connect the smoothing capacitor and the inverter, and - a housing configured to house the inverter, the smoothing capacitor and the first conductor portion; - the housing comprises a base portion having a mount surface on which the inverter and the smoothing capacitor are mounted, - the base portion is made of an insulating resin material, - the housing comprises a cover portion made of metal material attached to the base portion to cover the inverter, the smoothing capacitor and the first conductor portion, and - the housing comprises a metal thin plate formed on a lower surface of the base portion opposite the mount surface, - the metal thin plate is larger than an outer shape of the lower surface of the base portion and functions as a bottom plate of the cover portion, - a stepped portion having an end surface abutted with the mount surface of the base portion is formed in an inside part of the side wall of the cover portion and a leading end surface of the side wall is abutted with an outer peripheral edge of the thin plate, - the first conductor portion is placed in the vicinity of or in contact with the mount surface of the base portion of the housing in the middle of connection between the smoothing capacitor and the inverter, and - the base portion comprises a first coolant flow passage through which a coolant that cools the inverter can flow which is formed below a part where the inverter is mounted.