PURPOSE: To achieve a higher detection accuracy with a reduction in effect of an extraneous noise, by forming an earth electrode either or both at a part surrounding a sensor element section and on a surface on the side where no sensor element section is formed.

CONSTITUTION: An earth electrode 8 comprising conductor pattern films 8A and 8B is formed in an area surrounding a sensor element section 7 on a surface on the side where the sensor element section 7 of a ceramic substrate 1 is located. The earth electrode 8 is also formed on an insulation layer 9 at a part corresponding to the top surface side of element terminal sections 5 and 6, surrounding the entire circumference of the sensor element section 7 and an earth terminal section 10 is extended from the earth electrode 8 to one side of the ceramic substrate 1. With such an arrangement, an extraneous noise signal arriving from the perimeter of the sensor element section 7 flows to the earth electrode 8 thereby achieving a reduction in the extraneous noise signal as picked up with comb-shaped electrodes 2 and 3 of the sensor element section 7 and with the element terminal sections 5 and 6.