A boom vibration control device (9) equipped with: a boom (4) which is axially supported by a raisable/lowerable base (3) so as to be rotatable a hydrostatic pressure cylinder (30) for biasing the boom (4) in a right roll direction and provided between the boom (4) and the raisable/lowerable base (3) and a metal spring (60) for biasing the boom (4) in a left roll direction and provided between the boom (4) and the raisable/lowerable base (3).