PURPOSE: To discontinue conventional fittings, to simplify the struture, and also to avoid damage of an insulator, by inserting a stepped screw into a hole of the insulator, and fixing it to a fitting part.

CONSTITUTION: A pair of platelike lead wire connecting terminals 30, 30' are fixed to a platelike ceramic insulator 29 provided with fitting holes 28, 28' chamfered 27, 27', in the upper and lower parts, into which stepped screws 33, 33' are inserted. The lead wire connecting terminals 30, 30' are provided with recessed parts 31, 31'. A temperature detecting base body 4 consisting of a thin film thermistor chip is connected to internal lead wires 5, 5', so that the end part of the element 4 can be stored in the recessed parts 31, 31'. These recessed parts 31, 31' can be formed easily by drawing. In this regard, the internal lead wires 5, 5' and the lead wire connecting terminals 30, 30' are connected by spot welding.