The present invention relates to a lift support device, which comprises a vertical frame, a support seat, an elastic mechanism and at least a friction compensating mechanism. A substrate of the vertical frame is installed with a pair of slide rails at two sides opposite to the support seat, the elastic mechanism includes at least a constant-force spring installed between the vertical frame and the support seat; and the friction compensating mechanism includes an adjusting unit installed on the support seat, and the distal end of the adjusting unit faced towards the substrate is connected with an elastic member and a wearing resistant sleeve; when the support seat longitudinally slides between two sides of the vertical frame, the friction between the wearing resistant sleeve and the substrate is additionally increased for compensating the insufficient elastic force or overly-large elastic force provided by the constant-force spring.