A vibration reducing device is attached to a structure and blocks sound transmitted through the structure. The vibration reducing device includes a unit structure having a target frequency band, the unit structure including a plurality of unit cells, each formed of an acoustic meta-material and having a different target frequency, the unit cells being connected through first bridges; and a predetermined number of unit structures being connected through second bridges and attached to the structure, where each of the unit cells comprises: a mass portion of which a size is set according to the target frequency; a base frame formed as a quadrangular frame, the mass portion being eccentrically disposed in the base frame; and a support portion that connects the mass portion and the base frame, the support portion having a size that is set according to the target frequency.