To improve punching efficiency by permitting continuous punching operation without stopping a machine even if the width of a work has errors.

A required punching reference plane is selected from a plurality of reference planes, α, β, γ for each of holes to be punched, Q1, Q2, Q3, Q4. The punching operation is carried out according to the selected reference plane. In this case, (1) before punching, the required punching reference plane is selected from a plurality of reference planes for each of holes to be punched, (2) in punching, the width of the work part including the position of the hole to be punched is detected, (3) then, the punching operation is carried out based on the detected width of the work part according to the selected reference plane.