The dynamic vibration absorber is well known as a kind of passive-type vibration control device, where the mass and the stiffness elements basically comprise 1-dof system. Despite the reliability and the simplicity in constitution, the absorber does not work effectively for unexpected disturbances. The use of the absorber with fixed property is usually limited to a harmonically excited case, where the damper is only effective for pre-determined narrow frequency range. The damper design following well-known optimal tuning theory can extend the effective range, whereas the damping performance remains at a certain amount and yet the vibration caused by transient disturbances cannot be reduced sufficiently. A frequency-tunable dynamic absorber incorporating element with variable stiffness property can be a measure for placing adaptability to the structure against non-stationary disturbances, but the realization of such variability would be mechanistically complex and the problem of response time may become an issue. The Magneto-rheological elastomer (MRE) is known as a class of smart materials whose elastic property can be varied by the applied external magnetic field. In this paper, the MRE is adopted as the stiffness element in the dynamic absorber whose natural frequency is tunable by the external magnetic field. Both numerical and experimental investigations show that the vibration of 1-dof structure can be fully reduced by the proposed dynamic absorber with variable stiffness functionality.