A nitric oxide administration device 25 includes a second flow path 201 including an intake port 201a and an NO supply port 201b, a discharge unit 205 which is arranged in the second flow path 201 and which generates NO from air introduced via the intake port 201a, generated NO being supplied via the NO supply port 201b, an NO2 adsorption unit 206 which is arranged downstream of the discharge unit 205 and which removes NO2, an NO densitometer 208 which is arranged downstream of the discharge unit 205 or which is arranged in a flow path for reflux from downstream of the NO2 adsorption unit 206 to upstream of the NO2 adsorption unit 206, and a concentration estimation unit 301 which estimates an NO concentration and an NO2 concentration in a predetermined position based on an oxygen concentration in the atmosphere or the second flow path 201, an NO concentration measured by the NO densitometer 208, and a residence time of gas containing NO in the second flow path 201 between the NO2 adsorption unit 206 and the predetermined position.