The nitrogen oxide analyzer obtains the ozone concentration-luminescence response characteristics that show the relationship between the ozone concentration and the light intensity by chemiluminescent response obtained by varying the ozone concentration alone in a steady state, and sets the relationship of the parameter that determines an average period of the sample gas passing the reactor so that the luminescence response is generated in the reactor alone even though the ozone concentration of the ozone-containing gas changes within a predetermined range based on the ozone concentration-luminescence response characteristics.