An electric circuit device includes a noise generating circuit unit which generates noises, a housing which stores the noise generating circuit unit thereinside, is electrically earthed, and includes an opening, a control board which is provided with a connector to connect a wiring to an outside, a base plate which is disposed between the noise generating circuit unit and the control board to cover the opening of the housing, and a high impedance component which has impedance higher than the base plate against the noises. The base plate includes a first base plate which supports the control board, and a second base plate which is separated from the first base plate. The first base plate and the second base plate are disposed to interpose the high impedance component therebetween.