The nonlinear mechanical modulator of the present invention comprises first and second masses, a first spring connecting the first and second masses, and a second spring connecting the second mass and a fixed end. A motion input is applied to any one of the first and second masses and a resultant motion output is generated from the other one of the masses. Further, at least one of the springs has a nonlinear behavior characteristic that its stiffness varies according to a magnitude of the motion input. At this time, a nonlinear characteristic of the spring is categorized into a nonlinearly increasing characteristic that its stiffness is increased as its deflection becomes greater, and a nonlinearly decreasing characteristic that its stiffness is decreased as its deflection becomes greater. One or both of the two nonlinear characteristics can be applied to and employed in the mechanical modulator of the present invention.