The embodiments provide a method making it possible to safely and inexpensively measure concentrations of combustible gases, such as methanol, at room temperature even in high concentration atmospheres, and also provide a sensor making it possible to carry out the above measurement method. The measurement method comprises: arranging a film containing nanoparticles of tungsten oxide and a pair of electrodes which are separated from each other and which individually keep in contact with said film in said atmosphere, exposing said film to light, measuring electric resistance change of said film before and after exposing said film to light, and determining said concentration based on said change.