A support device adjustable with an electric motor for supporting the upholstery of a piece of seating and/or reclining furniture, in particular a mattress of a bed, with a base part, with a support part, which is connected to the base part so as to be pivotable about a first pivot axis, and with an electromotive drive device, which is in operative connection with the base part and the support part for pivoting adjustment of the support part relative to the base part, wherein the base part and the support part are configured and operatively connected to the drive device in such a way that the support part can be adjusted between an unadjusted starting position, in which the support part rests flat on the base part, and an end position of the adjustment movement, in which the support part is arranged at an angle to the base part, characterized in that the electromotive drive device has a spindle drive which has a stationary, rotatably mounted threaded spindle which is in rotary drive connection with an electric motor of the drive device and on which is arranged a spindle nut which is movable in the axial direction of the threaded spindle and forms the output member of the electromotive drive device, in that at least one first wedge-like lifting guide element (20, 20') is arranged on the base part in the region of the first pivot axis and at least one second wedge-like lifting guide element is arranged on the support part opposite the first wedge-like lifting guide element (20, 20'), and in that the lifting guide elements (20, 20', 22) are arranged in the path of movement of a free end of a plunger, the other end of which is connected to the spindle nut in an articulated manner and pivotably about a second pivot axis parallel to the first pivot axis in such a way that the free end of the plunger presses against the lifting guide elements (20, 20', 22) in order to pivot the support part relative to the base part. with a base part, with a support part, which is connected to the base part so as to be pivotable about a first pivot axis, and with an electromotive drive device, which is in operative connection with the base part and the support part for pivoting adjustment of the support part relative to the base part, wherein the base part and the support part are configured and operatively connected to the drive device in such a way that the support part can be adjusted between an unadjusted starting position, in which the support part rests flat on the base part, and an end position of the adjustment movement, in which the support part is arranged at an angle to the base part, characterized in that the electromotive drive device has a spindle drive which has a stationary, rotatably mounted threaded spindle which is in rotary drive connection with an electric motor of the drive device and on which is arranged a spindle nut which is movable in the axial direction of the threaded spindle and forms the output member of the electromotive drive device, in that at least one first wedge-like lifting guide element (20, 20') is arranged on the base part in the region of the first pivot axis and at least one second wedge-like lifting guide element is arranged on the support part opposite the first wedge-like lifting guide element (20, 20'), and in that the lifting guide elements (20, 20', 22) are arranged in the path of movement of a free end of a plunger, the other end of which is connected to the spindle nut in an articulated manner and pivotably about a second pivot axis parallel to the first pivot axis in such a way that the free end of the plunger presses against the lifting guide elements (20, 20', 22) in order to pivot the support part relative to the base part.