Metamaterial is artificial materials in which minute structures (meta-atoms) are arranged with a period shorter than wavelength of the wave of interest. By controlling the wave propagation behavior, physical behaviors not found in nature, such as a negative refractive index, are exhibited in a specific frequency range. The propagation behavior of sound waves is governed by effective mass density and effective bulk modulus. Locally resonant acoustic metamaterials are metamaterials that target sound waves, using a spring-mass-type resonator as a meta-atom. This type of acoustic metamaterials can control the effective mass density depending on the material and structure, and exhibits unique properties. The acoustic metamaterials with meta-atoms comprised of silicone rubber and steel cylinder, showed remarkable vibration reduction and high sound insulation performance exceeding the mass law in the designed frequency range. It is expected to be high vibration reduction and sound insulation materials.