Abstract: A housing (3) has an upper end wall (3a) which supports an upper slide portion (11) of a clamp rod (5) vertically movably. The housing (3) has a lower end wall (3b), a support cylinder (13) of which supports a lower slide portion (12) of the rod (5) vertically movably. The rod (5) is provided with an input portion (14) between the upper slide portion (11) and the lower slide portion (12). A clamp spring (20) connected to the input portion (14) drives the rod (5) downwards for clamping. The lower slide portion (12) has an outer periphery provided with a helical rotary groove (27) and a straight groove (28) which is in upward continuity with the rotary groove (27). A ball (29) engages with the rotary groove (27) and the straight groove (28). The ball (29) is supported by an inner wall (13a) of the support cylinder (13).

Abstract: A pillar (3) is projected upwardly from a central portion (2) of a base plate (1), and at least two work receiving portions (4) (4) are disposed in the opposite sides of the peripheral portion of the base plate (1). A plurality of pressing arms (5) (5) are projected radially from the pillar (3) toward the work receiving portions (4) (4), and these pressing arms (5) (5) are supported horizontally pivotally by the pillar (3). A pressing hydraulic cylinder (6) is disposed in the projecting portion of the pressing arm (5) so as to face downwardly.