PURPOSE: To improve fastening accuracy of a vice.

CONSTITUTION: A fixed jaw 4 is fixed on a frame 2, and a moving jaw is provided in opposition to the fixed jaw 4 on the frame 2 so that the moving jaw can be moved in the fastening direction, while a hollow support shaft 6 is composed of a rear support shaft 6e and a front support shaft 6f. A first surface 6b that can be slid in the fastening direction is provided on the frame 2, and the rear part of its rear support shaft 6e is threaded with the moving jaw, while the first surface 6b directing in the rear part is provided in the fore part of the front support shaft 6f, and a supporting member 12 fixed to the frame 2 is engaged with the front support shaft 6f, and the rotation thereof is inhibited thereby, and a second surface 12b directing in the front part is formed. A pressure power transmission member 18 inserted in the support shaft 6 is connected to a pressure power generation mechanism in the rear part, while a power increase mechanism 30 connected to the front end of the pressure power transmission member 18 below the fixed jaw 4 is put between the first and the second surfaces, so that it can be in contact by pressure with both of the surfaces.