GAS ANALYZER

A gas analysis apparatus (100) includes: one light emitting unit (2) arranged outside a gas flue wall (la); a first reflector (3) that reflects measurement light that has been emitted from the light emitting unit (2) and has been transmitted through the sample gas (Sg); a light receiving unit (4) arranged outside the gas flue wall (1a) that receives the measurement light that has been reflected by the first reflector (3); a second reflector (5) arranged outside the gas flue wall (1a) that reflects the measurement light toward the light receiving unit (4); a known substance containing unit (6) arranged in a space along the light path between the light emitting unit (2) and the second reflector (5) that contains the known substances, a computing unit (7) that analyzes sample gas (Sg) by allowing the measurement light emitted from the light emitting unit (2) to be reflected by the first reflector (3) and performs correction or calibration of the gas analysis apparatus (100) using the known substances by allowing the measurement light emitted from light emitting unit (2) to be reflected by the second reflector (5); and a switching unit (8) arranged outside the gas flue wall (1a) that removes the second reflector (5) from the light path when performing the component concentration and places the second reflector (5) into the light path when performing the correction or calibration.