A magnetic device for gripping and clamping workpieces, in particular sheet-steel elements (L), comprises a supporting casing (2), slidably mounted within which is a magnet-holder member (4) carrying a main permanent magnet (M). The magnet-holder member (4) can be displaced between an advanced, operative, position, in which the main magnet (M) is designed to grip and clamp a workpiece (L), and a retracted, inoperative, position. The movement of the magnet-holder member (M) is controlled by shape-memory actuator means (A1, A2, B, E).