This paper deals with the forced nonlinear vibration, its stability and the effects of vibration isolation of a new type of mechanical damper, which is attached to a single-degree-of-freedom-system, theoretically, experirnentally and by means of digital simulation. The damper which is composed of a ball screw, a flywheel and a vertically oscillating governor is further simplified in its structure and is more effective in suppressing the resonance of the primary system as compared with the former type which uses a flyball governor instead of the vertically oscillating governor. The results may be summarized as follows: (1) Resonant amplitude of the primary system may be fairy decreased by the oscillation of the 90vernor. (2) The nonlinear solution differs from the linear one which is solved by regarding the 90vernor as a flywheel. (3) Stable solutions for the primary system and the governor are obtained when the forcing frequency is lower than the natural frequency of the governor. (4) Theoretical results agree well with the simulated values. (5) Effects of vibration isolation of the damper are also verified experimentally.