An infrared gas sensing apparatus for sensing gas includes an infrared source for emitting infrared light, a wavelength tunable filter for selectively allows passage of the infrared light at a specific wavelength, an infrared detector for detecting the amount of the filtered infrared light, and a control circuit for controlling the wavelength tunable filter. The control circuit has a check circuit that checks whether the wavelength tunable filter selects a collect wavelength. The check circuit controls the wavelength tunable filter so that the wavelength tunable filter allows passage of the infrared light at a wavelength within a wavelength range where atmospheric gases do not absorb the infrared light. The check circuit checks whether the wavelength tunable filter operates normally by comparing the amount of the filtered infrared light with a reference value.