The present invention relates to an apparatus for gas sensing including: a header part to generate interference wave to light from light source by the principle of fiber fabry-perot interferometer; and an optical spectrum analyzer to decide existence of specific gas based on change of spectrum periodicity of the interference wave, wherein the header part includes a sensing material that expands or shrinks by the above specific gas and the above interference wave changes its spectrum periodicity depending on expansion and shrinkage of the above sensing material.