An infrared sensor for detecting infrared rays of light and a light emitting element are disposed below a light transmittable top plate, which has a hearing area for heating an article to be heated placed thereon, in juxtaposed fashion relative to each other, so that infrared rays of light radiated from the article to be heated may be guided towards the infrared sensor. A light guide portion is provided for guiding rays of flight, emitted from the light emitting element, towards a heating area of the top plate, and the rays of light emitted from the light emitting element and guided by the light guide portion are projected onto the top plate through an upper opening of the light guide portion so that such rays of light can be noticed with eyes within the heating area.