PURPOSE: To improve follow-up properties with a simple mechanism by moving a touch sensor through a program, detecting whether the touch sensor and the middle point of a stock to be worked come into contact or not by whether the electric current is on or off and controlling compressed gas supplied to a pressure room.

CONSTITUTION: When the metallic stock 5 to be worked and the touch sensor 6 come into contact through a touch plate 6a, electric current flows among a contact signal generating device 11, the stock 5 to be worked and the touch sensor 6 and when they do not come into contact, the electric current does not flow. The controller 9 commands a speed specified by a creep program to a driving apparatus 7 for the stock 5 to be worked contained in a data base 8. The touch sensor 6 is moved by the program contained in the data base 8 in the advancing direction of creep at a desired speed through a variable speed driving apparatus and quantity of compressed gas sent into the pressure room 3 is controlled automatically by whether the current in a contact signal generating device 11 is on or off and followed by the touch sensor 6 to control the creep speed of the stock to be worked.