Abstract: A machine vice with force amplifier comprises a base member (1) with an upwardly open, elongated recess (2), a fixed jaw (4) arranged at one end (1a), which is unitary with the base member (1). A movable jaw (5) is slidably mounted on the base member (1) and bears on its under side a unitary projection extending into the recess (2), with a spindle nut (7). A tightening device (8, 9) is arranged in the recess (2), consisting of a screw spindle (8) with force amplifier engaging in the spindle nut (7), which are adapted to be driven by a common handle (15). On the other end (1a) of the base member (1) a reaction plate (11) is fixed by a plurality of screws (12) on a fixing surface (14) ewxtending perpendicular to the spindle axis (A), against which plate the tightening device (8,9) abuts. The base member (1) comprises a second fixing surface ( 14a) for the reaction plate (11) at its one end (1a) and corresponding threaded bores (13a) for its screws (12).