To improve a shearing ratio by automatically regulating inversion timing for a ram direct after the collection of cutting regardless of the plate thickness and cutting position of a workpiece.

A back gauge device 27 for positioning a cutting length is provided on a shearing device 1. Since the device 27 and a lower blade 7 are electrically connected to a current detection device 41 via a connecting wire 43, the striking of a workpiece W against the device 27 carries a current between the blade 7 and the device 27 via the workpiece W. When this current- carrying is detected by the device 41, a command that an upper blade 23 be lowerd is imparted from a control device 37, and the workpiece W is cut, the current-carrying is cut off, so that the shearing work is judged to be finished and a command that the blade 23 be immediately raised is given to a hydraulic cylinder 17.