PURPOSE: To ensure watertightness between a casing lid body and a casing body while facilitating the assembling.

CONSTITUTION: A easing lid body lock screw 59 is screwed down on a easing lid body lock plate 60 so that a cover expansion part 54 of the easing lid body and a lock screw fixing part 46 are held being grasped between the head part of the easing lid body lock screw 59 and the casino lid body lock plate 60. In tap this manner, the casing lid body is mounted on a casing body so as to allow loading or unloading. A mounting hole 90 is cut into a U-shaped angular part of the lock screw fixing part 46 while a fixing screw part 91 is provided at a fixing member mounting part 63 where a universal cord is mounted at a position facing the mounting hole 90 of the lock screw fixing part 46. The mounting hole 90 and the lock screw part 91 are joined together withe mounting screw 92 being in a matched state.