The cavitation process is performed on the inner surface of the target hole. The cavitation processing method includes; attaching a cap (50) having a through hole (58) to an inlet (21) of a target hole (20e) of a workpiece (10e); immersing the workpiece (10e) and a nozzle (102) into a processing liquid; and ejecting a jet of the processing liquid from the nozzle (102) located outside of the target hole (20e) to an inside of the target hole (20e) through the through hole (58) such that a cavitation process is performed on a processing region (A1e) that is located downstream of a non-processing region (B1e, B2e) covered by the cap (50) on an inner surface of the target hole (20e).