To reduce a cost and to improve work efficiency by allowing only a thermoswitch to be replaced even in the case where a sensor is mounted in a liquid when a failure or the change of a temperature condition occurs in a thermoswitch.

The thermoswitch 1 being a sensor for temperature control is inserted into a sensor case 2 with a replaceable structure. Wires of the thermoswitch are connected to a terminal block 3. A plurality of the replaceable thermoswitches 1 are incorporated in the sensor case as required. Another embodiment is characterized in that a temperature regulator (electronic circuit)11 using a thermal sensor 10 instead of the thermoswitch 1 is incorporated in the replaceable sensor case 2 or a terminal box 4. The thermoswitch is formed into a structure having a function of a water level sensor 6 as required.