A scrub washing apparatus comprises a spin chuck for holding a substrate to be processed substantially horizontally, a nozzle for supplying a washing liquid to the substrate mounted on the spin chuck, an arm vertically and horizontally movably supported, an output shaft provided at the arm, a sponge brush connected directly or indirectly to the output shaft, for scrubbing the substrate on the spin chuck in contact therewith, a press mechanism moving the sponge brush downward together with the output shaft, for pressing the sponge brush against the substrate on the spin chuck, and a rotation drive mechanism provided above the press mechanism at a position where the rotation drive mechanism is capable of being engaged with the output shaft, for directly rotating the sponge brush by engaging with the output shaft.