The invention refers to a sheet processing apparatus and an image forming system, which can restrain cutting wastes from being charged without leaving the sheet excessively wet. The sheet processing apparatus (20) possesses a punching part (40) used for cutting part of a piece of paper (P) used as a processing object along a conveying path; and a humidifying part (30) configured on the upstream side of the punching part (40) in the conveying path and used for selectively humidifying a designated area (Ra) of the paper (P) including a punching area (Pa) cutting the punching part (40) from the paper (P) to be transferred.