To prevent a work from receiving flaws when it is conveyed by setting a time for opening a main body vise and making a controller activate a driving device of the main body vise for a setting time.

A digital switch 33 is primarily fixed for setting a frequency of feed but it is also used for adjusting an amount of jogging for opening of a main body vise by changing a selector switch 35; a timer in a sequencer 25 is controlled by the digital switch 33 to set a time for turning on a loosening relay 29 so as to turn on a loosening solenoid 19. The loosening solenoid 19 and a tightening solenoid 21 is activated for a command time of jogging for opening to activate a cylinder of the main body vise, thereby opening the main body vise by the desired amount of jogging for opening.