A substrate processing apparatus processes a surface of a substrate with a processing fluid and includes a support tray in which a concave part for housing the substrate is provided on an upper surface thereof; a storage container in which a cavity is formed, wherein the support tray may be stored in a horizontal posture in the cavity; and a fluid supply part supplying the processing fluid to the cavity, wherein the storage container has a flow path which receives the processing fluid and discharges the processing fluid in a horizontal direction into the cavity from a discharge port that opens on a side wall surface of the cavity and toward the cavity, and a lower end position of the discharge port in a vertical direction is the same as or higher than a position of the upper surface of the support tray stored in the cavity.