A fluid supply nozzle includes a fluid flow-in section into which a fluid flows in, a reservoir section for storing the fluid, a flow velocity control wall provided between the fluid flow-in section and the reservoir section and including an orifice for making the fluid flow in the reservoir section while reducing a flow velocity, and a discharging section including a slit for discharging the fluid with pressure of the fluid applied to the reservoir section. A substrate processing apparatus is formed so as to include the fluid supply nozzle. Moreover, a substrate processing method includes the step of discharging a fluid in a single-layered, continuous film to supply the fluid onto a substrate. Thus, the substrate is processed. To perform this method, the fluid supply nozzle of the present invention can be used.