To provide a sheet binding processing apparatus for enabling strong binding strength or weak binding strength to be selected in a neat sheet posture to perform binding processing in applying narrow pressure to a plurality of sheets with concavo-convex-shaped pressurizing surfaces to perform the binding processing, in positioning sheets in a binding position for press-binding the sheets with the concavo-convex-shaped pressurizing surfaces that mutually mesh to perform the binding processing, it is possible to set an engagement area of the sheets and the pressurizing surfaces in two or more different steps with positioning references or by shifting a position of a binding processing section in the direction for passing over an edge side of the sheets to perform the binding processing.