PURPOSE: To prevent the torsion of a coil spring from occurring.

CONSTITUTION: A level switch has a read switch 51 within a central cylindrical part of a main body 50, the switch 51 is connected to a connector 56 through a lead wire 55, and the connector 56 is connected to a control panel through an outer cable. A float 53 made of plastics with a built-in magnet 52 is pooided outside the cylindrical part. A thin coil spring 54 of about 0.3mm in diameter is provided inside the lower end of the float 53, and in the outside thereof, a protector 61 integrated with a stopper is fixed in the main body 50 with a thread 62. A notch for receiving a stopper for preventing float rotation is provided outside the float 53. A proper number of water passage holes 63 is bored through the bottom of the protector 61.