PURPOSE: To maintain an excellent contact state between a laminate heater and a temperature sensor by forming the part of the laminate heater which faces the temperature sensor in a recessed shape.

CONSTITUTION: The laminate heater 15 has downward projecting recessed parts 23 and 24 formed opposite a thermistor 21 and a temperature fuse 22. The recessed parts 23 and 24 are formed as grooves extending from one end of the laminate heater 15 to be other end and abut on the top surface of the thermistor 21 and temperature fuse 22 in an air insulating layer 4 to press those thermistor 21 and temperature fuse 22. The thermistor 21 and temperature fuse 22 securely contact the heater 15 and the recessed parts are formed in a bent shape and never deform. Consequently, the laminate heater is prevented from curving to float and the contact state between the laminate heater and temperature sensor is maintained excellently and temperature sensing accuracy can be held high.