Abstract: A boom damping device includes a fluid pressure cylinder configured to perform an expansion/contraction operation in conjunction with rotational movement of a boom in a roll direction of a working vehicle, a first pressure accumulator into/out of which an operating fluid flows through a first passage with the expansion/contraction operation of the fluid pressure cylinder, a second pressure accumulator into/out of which the operating fluid flows through a second passage with the expansion/contraction operation of the fluid pressure cylinder, and a shut-off switch configured to shut off the first passage and configured to shut off the second passage if at least either one of a right boom and a left boom is not at a working position expanded in a right-and-left direction of the working vehicle.

Abstract: A boom vibration control device that is configured to suppress vibration of a boom that is cantilever-supported on a working vehicle includes a left-roll-direction biasing unit that biases the boom in the left roll direction with respective to the working vehicle and right-roll-direction biasing unit that biases the boom in the right roll direction with respective to the working vehicle. The boom is held at the roll angle at which the biasing force of the left-roll-direction biasing unit and the biasing force of the right-roll-direction biasing unit are balanced.

Abstract: A boom raising and lowering device that is configured to raise and lower a boom includes a raising and lowering mount that is provided so as to be able to be raised and lowered with respective to the working vehicle, a roll mount that is provided on the raising and lowering mount so as to be rotatable in a roll direction and that supports the boom in a cantilever-supported manner, a first raising and lowering actuator that drives one end of the roll mount in the vertical direction with respective to the working vehicle, and a second raising and lowering actuator that drives other end of the roll mount in the vertical direction with respective to the working vehicle. The boom is driven in the vertical direction and roll direction by operating the first raising and lowering actuator and the second raising and lowering actuator.