PURPOSE: To achieve a higher reliability, by forming a fine-dia. section at a part of an electrode along the length thereof to eliminate mechanical deformation during the energization of a hot wire.

CONSTITUTION: Fine dia. sections 20 and 20 are formed at parts of electrodes 6a and 6b along the length thereof in a gas rate sensor. When a hot wire 7a is energized, possible mechanical deformation can be prevented as an extension portion caused by thermal expansion of the wire 7a can be absorbed by bending to the electrodes 6a and 6b owing to pliability thereof. Then, a stable rate output signal can be obtained starting from the energization.