PURPOSE: To bend a thick plate material by a small pressure capacity by increasing and decreasing repeatedly a stroke speed of a metallic die in the vicinity of its end terminal, at the time of a stroke action of the metallic die.

CONSTITUTION: Various prearranged stroke speeds set to a setting part 9 are determined by an opened degree or a closed degree of each valve 81bW85b based on a pulse signal. A stroke end is detected by a signal from a position detector 12. In the stroke end, a vibratory pressure is applied to a base material by executing an opening and closing control of a servo-valve 8 by a minute period within a minute stroke range, without applying an excessive pressure as usual.