To improve the silence by adjusting spring constant to oscillatory input in the lateral direction in addition to oscillatory input in the vertical direction of a vehicle of a dynamic damper, moving resonance frequency in both directions to a high frequency side and inhibiting the oscillation.

This dynamic damper 10 comprises a rubber bush 11 composed of an inner cylinder fitting 12, an outer cylinder fitting 15 and a rubber elastic body 21 for elastically connecting the inner and outer cylinder fittings, and a cylindrical mass fitting 25 into which the outer cylinder fitting 15 of the rubber bush 11 is press-fitted. The inner cylinder fitting 12 has an annular flange part 14 extended to a radial outer part at its axial one end. The flange part 14 of the inner cylinder fitting 12 is fixed to a fastening face 32b of a mounting member 31 as a transmission-side bracket. An outer peripheral edge of the flat fastening face 32b kept into contact with the flange part 14, surrounds one end outer peripheral edge of a main body 13 of the inner cylinder fitting 12.