PURPOSE: To stabilize measurement by forming the same second conductor pattern group as a conductor pattern on the other surface of an insulating substrate and electrically connecting the corresponding conductor patterns and the second conductor patterns.

CONSTITUTION: Corresponding to the group of the conductor patterns 3 provided on one surface 1a of an insulating substrate 1, the group of the second same conductor patterns 4 is formed on the other surface 1b thereof and the corresponding conductor patterns 3, 4 respectively formed on the same regions of both surfaces are electrically connected at both side end parts 5, 6. By this constitution, the coefficients of thermal expansion of the metal membranes 7 - 9 formed on both surfaces of the insulating substrate 1 are made almost equal to prevent the generation of strain in the insulating substrate 1 due to a temp. change and the cross-sectional areas of the conductor patterns are increased to reduce electric resistance and stable measurement can be performed.