The invention relates to an apparatus for supplying NO (1), such as an NO/N2 gaseous mixture, comprising a main gas circuit (40; 40.1, 40.2) with flow rate control means (42, 43) comprising at least one main solenoid valve (42) operated by the operating means (50) in order to control the flow rate of NO/N2 mixture passing through said at least one main solenoid valve (42). The main solenoid valve (42) is a proportional solenoid valve having degrees of opening of between 0 and 100%, and is configured to function in at least two given operating ranges corresponding to different degrees of opening of the main solenoid valve (42). The operating means (50) are configured to control the main solenoid valve (42) in pulsed mode in one of the operating ranges so as to deliver successive gas pulses (IG) and in proportional mode in another operating range.