PURPOSE: To maintain TCR characteristics of a platinum wire and contrive reinforcement of tension strength thereof in regard to a very fine resistance wire, which is the platinum wire, using for a comparative element and a detection element of a contact combustion type CO sensor. CONSTITUTION: At least a pair of first terminal pins and a pair of second terminal pins 2b are projected at the surface side of a sensor base 1. A very fine resistance wire of a detection element for detecting CO concentration by contact reaction is tensed between the first terminal pins. Similarly, another very fine resistance wire of a comparative element 4 is tensed between the terminal pins 2b. The comparative element 4 and the detection element is partitioned by a partition plate 6. The very fine resistance wire of the comparative element 4 and the detection element is constituted by the platinum wire containing zirconia or yttria of a very small amount in the range of 1.0%, or less, tension strength is heightened twice compared with a conventional platinum wire and TCR characteristics equal to a pure platinum wire is secured.