The jack for the change of a position of the seat base in a wheelchair, characterized by the fact that in the lower frame (1) the driving system of the screw jack with a vertical screw (14) is fixed； and the upper end of the screw (14) is pivotally fixed in the main arms (3) of the scissors system. The driving system of the screw (14) of the screw jack is fixed to the base (11) attached slideably to the lower frame (1) in the tracks (8) in such a way that the screw (14) is permanently in a perpendicular position to the lower frame (1) and the upper frame (2) with maximum deviation of ±10°； and the base (11) is driven by the arms (17), with their first ends fixed pivotally in the main arms (3), and the other ends fixed pivotally in the base (11). The driving system of the screw (14) of the screw jack consists of the engine (9), which drives the nut (10) of the screw jack by means of gear transmission, and in the gear transmission a small wheel (13) is positioned on the engine pivot (9), and the big wheel (12) is joined coaxially with the nut (10). The engine (9) is an electric engine. In the driving system of the screw jack two engines (9) are used, simultaneously geared with a gear wheel (12), of the nut (10). The driving engines (9) are electric engines. The screw (14) of the screw jack is fixed to the main arms (3) by means of a bed (15) fixed pivotally in the main arms (3) of the scissors system.
