Cargo Bed Raising and Lowering Apparatus of Dump Truck

When a tilt in a right-and-left direction occurs in a cargo bed () being raised due to imbalance of excavated materials, the tilt is detected as a roll angle (θR), and it is determined whether the absolute value (|θR|) of the roll angle is not less than an imbalance determination value (θ) (S). When the absolute value is not less than the imbalance determination value (θ) (Yes in S) and the roll angle (θR) is positive (the cargo bed () is rising to the right) (Yes in S), an oil supply amount (VL) to a hoist cylinder () on the left side is increased, and an oil supply amount (VR) to a hoist cylinder () on the right side is decreased (S). When the roll angle (θR) is negative (the cargo bed () is rising to the left) (No in S), the oil supply amount (VL) on the left side is decreased, and the oil supply amount (VR) on the right side is increased (S).