PURPOSE: To expand a detecting area and to detect flames over a wide range by arranging plural detecting tubes so that the directions of detecting areas of plural detecting tubes are different from each other.

CONSTITUTION: Two detecting tubes 2 for detecting ultraviolet rays or infrared rays radiated from flames are arranged on the outer surface of a housing 1a. The tubes 2 are electrically connected to a processing circuit base built in the housing 1a. The detecting area of one detecting tube 2 is approximately conical and has about 110° angle of visual field. The two tubes 2 are arranged so that the detecting area of one tube 2 is overlapped on that of the other tube 2 by 20° angle of visual field. The pointing direction of respective tubes 2 are set to be 90° apart from each other. Thereby ≥180° angle of visual field can be continuously secured as the detecting area of a flame sensor 1.