A substrate processing apparatus has a two-fluid nozzle having an inner cylindrical member and an outer cylindrical member. Gas flows in the inner cylindrical member which is a gas passage and the processing liquid downwardly flows in a processing liquid passage constituted of the inner and outer cylindrical members. The gas and the processing liquid are mixed in a mixing area below the inner cylindrical member to generate fine droplets, and the droplets are ejected from an outlet of a lower end of the outer cylindrical member onto a substrate. Charge is induced on the processing liquid by generating an electric potential difference between a first electrode provided in the gas passage and a second electrode provided in the processing liquid passage, to generate charged droplets. In the nozzle, the first electrode is isolated from the processing liquid with a simple construction, and the droplets can be charged efficiently.