PURPOSE: To adjust a temporal interval between a fixed jaw and a movable jaw clamping a workpiece between them to a dimension of the workpiece approximately so as to carry out efficient setting by means of simple operation.

CONSTITUTION: A fixed jaw is arranged on the front end side of a base 6, while on the rear end side, a pressing part provided with a movable jaw is arranged freely advancingly. A rack type teeth 16 are arranged along the longitudinal direction of the base 6 in one side part of the base 6. A crest shape of the rack type tooth 16 is constructed of continuing an orthogonal face 19 perpendicularly intersecting the base 6 and a slanting face 21 slanting to the fixed jaw side. A jaw member 23 to be engaged with the orthogonal face 19 is arranged in a holder part 22 provided in the pressing part facing the rack type tooth 16. The engaging condition of the jaw member 23 can be released when a releasing lever 25 arranged in the holder part 22 parallelly to the base 6 is pulled. By means of an energizing action of a coil spring 59, the jaw member 23 is held in an engaging condition with the rack type tooth 16.