In an electric connection box, even if accuracy of a relative position between a first screw passage hole and a first screw hole, as well as accuracy of a relative position between a second screw passage hole and a second screw hole, is low, the relative positional relation between the first screw passage hole and the first screw hole, as well as the relative positional relation between the second screw passage hole and the second screw hole, can be adjusted because of the provision of a gap between an outer peripheral surface of a constricted engagement portion of a provisionally-placing projection and a hole-defining peripheral surface of a mounting member at the time of mounting a connection box body on the mounting member so that the passage of a first screw through the first screw passage hole and the first screw hole, as well as the passage of a second screw through the second screw passage hole and the second screw hole, can be easily carried out.