PURPOSE: To obtain a certain damper effect in a wide frequency band for a dynamic damper comprising a mass of quantity m2 resonated at a frequency (f) and a spring of a spring constant of k2, by forming it in such a way that an expression k24π2f2m2 is satisfied in an aimed vibrational frequency region.

CONSTITUTION: The vibration of an engine is input into an outer cylinder 5 of an engine mount insulator, and an insulator rubber 6 is elastically deformed, while a sealed liquid reciprocates between inner and outer chambers 7 and 8, against the flow resistance of an orifice 9. During this process, dynamic spring has a mass of quantity m2 by which the engine is resonated at a frequency (f), while an insulator 1 is a spring of a spring constant k2, and an expression k24π2f2m2 is to be satisfied. The frequency characteristic of the constant k2 is an engine resonance line indicated by a dotted chain line shown in the figure 1, and as long as the spring constant k2 is varied along the engine resonance line, in relation to the frequency (f), a sufficiently dynamic effect can be obtained. By defining this frequency region as a practical frequency region, the entire vibration can be vibraionproofed.