An exhaust gas analyzer of the present invention includes a sensor unit 11 installed in an exhaust path from an engine, applies laser light to exhaust gas emitted from the engine and receives laser light that has passed through the exhaust gas so as to measure the concentration of a component contained in the gas based on the received laser light. To an aperture 16 formed in a sensor base 15 of the sensor unit 11, an adjustment ring 40 in a circumferential face of which small holes 41 serving as a laser light passage portion is formed and whose inner circumferential face serves as an exhaust gas passage opening 21 is detachably fitted, whereby the sensor unit can be attached so as to conform to different inner diameters of exhaust tubes.