A vibration damper device includes a pair of viscoelastic dampers, lower braces which support the viscoelastic dampers from below, upper braces which support the viscoelastic dampers from above, lower connection members which connect the viscoelastic dampers to the lower braces, upper connection members which connect the viscoelastic dampers to the upper braces, and first joining members and second joining members which join the pair of viscoelastic dampers. Each lower brace includes a lower recess which avoids interference with the central vertical frame, and a lower slit into which the lower connection member is inserted. Each upper brace includes an upper recess which avoids interference with the central vertical frame, and an upper slit into which the upper connection member is inserted.