To improve work efficiency and the service life of a movable blade by decreasing the number of cutting times in ripping work.

A shearing machine 2 is provided with a cutting part 8 comprising a fixed blade 12 and a movable blade 11 and a plate material feed part 6. A control mans 18 for ripping work has a means 20 determining a stroke amount of the movable blade 11 by one time in accordance with a thickness of a cut plate material W and a means 21 determining a feed amount of the plate material. The determining means 20 for the stroke amount determines it to an amount of the movable blade 11 lowering down to a height obtaining a fixed clearance relating to a surface of the plate material W.