In an upper surface of a bottom wall of a box body having a part accommodation room formed inside, a recess is provided. In the bottom of the recess, a bolt hole to fix an electrical junction box to a vehicle body is penetrated. In the upper surface of the bottom wall of the body hole, a flat sealing surface is formed to surround an opening of the recess. When an electronic unit is accommodated in the part accommodation room, the bottom surface of the electronic unit is brought into close contact with the sealing surface to close the recess, thus providing a seal between the part accommodation room and recess.