An inverter unit comprising component parts including at least an inverter and a filter which removes a high harmonic wave component from an output of said inverter, wherein said component parts are housed in an aluminum case having a bottom wall portion and a side wall portion, said filter includes a coil which is wound around a core extending straight and is arranged at a position closed to one end of said case, an end portion of said core being wound with said coil is arranged closed to an inner surface of said side wall portion of the case, and a ferromagnetic plate, which leads magnetic flux coming in and out said end portion of the core arranged closed to said wall portion of the case to the direction along the inner surface of the side wall portion of the case, is disposed between said end portion of said core and said inner surface of said side wall portion of the case.