Motor-operated jack for vehicle

A motor-operated jack for vehicles is disclosed. In the motor-operated jack of this invention, a lifting unit consists of a spiral lifting ram (105) having an internal thread (105a) limitedly formed at a lower portion of the spiral lifting ram (105), thus reducing its frictional resistance. A pin (103c) is held in a horizontal groove (103b) formed at the top end of a primary screw (103). This pin (103c) is slightly projected into two longitudinal holes (104c) symmetrically formed at the top portion of a secondary screw (104). A coil spring (103d), a spring cover (103e) and a snap ring (103f) are sequentially laid on the top of the pin (103c) such that the snap ring (103f) is seated in an annular groove (104d) formed on the inner surface of the top wall of the secondary screw (104), thus allowing the coil spring (103d) to bias the (103c) pin. This second screw (104) is thus prevented from being raised along with the spiral lifting ram (105). A support ram (107), having a top support (107a) and an external thread (107b), is movably fitted in a gap between the secondary screw (104) and the spiral lifting ram (105) while engaging with an internal thread (105c) of the spiral lifting ram (105) at the external thread (107b), thus allowing a user to control the moving stroke of the lifting unit as desired.