A closure device includes: a main body having first and second shoulders; a door secured rotatably to the main body and having first and second door edges; an engaging member; an engaging mechanism; and a second pivot axle. The first shoulder and the first door edge respectively have a through hole and a first axle hole. The engaging member and the engaging mechanism are disposed respectively at an inner side of the main body. The engaging member includes a first pivot axle extending through the through hole and the first axle hole, and a positioning piece extending radially from the first pivot axle and engaging the engaging mechanism. One of the second shoulder and the second door edge has a second axle hole, while the other of the second shoulder and the second door edge has the second pivot axle extending through the second axle hole.