A temperature detecting device includes a heat receiving plate, a displacement transmitting part, a deforming part, a deformation generating part and a displacement detecting part. The heat receiving plate is restrained at its rim portion to generate a displacement of a central portion in its thickness direction with respect to the rim portion in accordance with the temperature of an atmospheric gas. The displacement transmitting part is displaced in accordance with the displacement of the central portion of the heat receiving plate. The deforming part is deformed by the displacement transmitting part. The deformation generating part maintains a distance between the rim portion of the heat receiving plate and the deforming part. The displacement detecting part detects a deformation of the deforming part and outputs an electric signal.