An electric circuit device including a first high voltage serial connection circuit 2a and a second high voltage serial connection circuit 3a, those are provided on a board and connected to an end of high electric potential of a power source for automobile use; and a first low voltage serial connection circuit 2b and a second low voltage serial connection circuit 3b, those are provided on the board and connected to an end of low electric potential of the power source for automobile use, wherein the first high voltage serial connection circuit 2a and the second high voltage serial connection circuit 3a are respectively disposed on both surfaces of the board opposite to each other, and the first low voltage serial connection circuit 2b and the second low voltage serial connection circuit 3b are respectively disposed on the both surfaces of the board opposite to each other.