PURPOSE: To enable the generation of a partial temperature difference optionally on an insulation substrate by molding lead members in sizes differing from one another to set a junction position with the insulation substrate of the lead members to a posi tion corresponding to an operation temperature of a gas sensing section selectively.

CONSTITUTION: An insulation substrate 11 has gas sensing sections 12 and 13 on the surface of a plate. The substrate 11 is heated with a heater almost entirely, eventually causing gas sensing sections 12 and 13. The substrate 11 has pads 14 and 15 connected to the gas sensing sections 12 and 13 in such a manner as to be energizable electrically at four corners of the surface of the plate. A lead frame 16 and a lead wire 17 are connected thereto separately. The leads 16 and 17 are formed in large and small widths and arranged at parts near the respective gas sensing section 12 and 13. When the substrate 11 is heated, the leads 16 and 17 transmit heat thereof to radiate in large and small amounts. Thus, an ambinent temperature of the gas section 13 is raised higher than the ambient temperature of the gas section 12. Then, temperature of the gas sensing sections 12 and 13 having a difference of ΔT between operation temperatures T1 and T2 are made to reach the operation temperatures T1 and T2 almost simultaneously.