a pair of terminals 24 in place a lower fixing member 26 disposed in the lower compartment 23 to fix the other pair of terminals 24 in place and a u shaped rocking contactor 27 mounted at the center of the rear body 20 the upper fixing member 25 has a leg 251 extending to the center of the rear body 20 the lower fixing member 26 has a protuberance 261 on its top the rocking contactor 27 is formed at the bottom thereof with a protuberance 271 adapted to the protuberance 261 of the lower fixing member 26 a helical spring 28 is disposed in the u shaped rocking contactor 27 the cover 30 is adapted to engage with the rear body 20 so as to fix a button 31 in position then the cover 30 and the rear body 20 are connected together by two clamping members 40 and 41 the button 31 is provided in the front with a rectangular opening 311 embedded with light transmissive colored filter means 32 or the like and a hole 35 embedded with a transparent member 33 further the button 31 is formed with a cylindrical portion 34 extending from the rear surface thereof the.