PURPOSE: To make it possible to easily operate to exchange or change over electric parts by easily carrying out operation to replace globe lamps and to change over a frequency change switch.

CONSTITUTION: The inside wall surface of a main body case is provided with a substrate 32 packaged with the glow lamp 38 and the frequency change switch 34. This main body case 9 is provided with a waterproof cover 39 to cover the substrate 32 with plural tapping screws 40. An aperture 41 for working is formed in part of this waterproof cover 39 near the electric parts such as the glow lamp 38 and the frequency change switch 34, etc. This aperture 41 is provided with an attachable and detachable cap 42. The glow lamp 38 and the frequency change switch 34 are operated to be changed over or exchanged via the aperture 41 by such constitution without removing the waterproof cover 39 and the main body case 9.