A dump truck 1 comprising: a cooling oil 12 tank for storing cooling oil; a braking system 11 to which the cooling oil is supplied; a transmission 6 to which the cooling oil is supplied via the braking system; a first hydraulic pump 51 that is driven by an engine 5 and supplies the cooling oil in the cooling oil tank to the braking system and the transmission; a second hydraulic pump 52 that supplies the cooling oil in the cooling oil tank, in addition to the cooling oil from the first hydraulic pump, to the braking system and the transmission; characterised by a hydraulic motor 54 whose output axis is connected to an input axis of the second hydraulic pump; a hydraulic oil tank 24 for storing hydraulic oil; a third hydraulic pump 53 that is driven by the engine and supplies the hydraulic oil in the hydraulic oil tank to the hydraulic motor; a flow amount adjuster 55 that is provided along a bypass channel 28 that lets a predetermined amount of the hydraulic oil from the third hydraulic pump bypass the hydraulic motor and adjusts a bypass flow amount in the bypass channel; and a controller 57 that controls the bypass flow amount at the flow amount adjuster based on a brake status in the braking system, a capacity of the first hydraulic pump corresponding to a flow amount of the cooling oil required to lubricate the transmission, a capacity of the second hydraulic pump corresponding to a flow amount of the cooling oil to make up for the cooling oil from the first hydraulic pump in order to provide the cooling oil supplied when the braking system is in operation, and a capacity of the third hydraulic pump being smaller than a capacity of the second hydraulic pump. a cooling oil 12 tank for storing cooling oil; a braking system 11 to which the cooling oil is supplied; a transmission 6 to which the cooling oil is supplied via the braking system; a first hydraulic pump 51 that is driven by an engine 5 and supplies the cooling oil in the cooling oil tank to the braking system and the transmission; a second hydraulic pump 52 that supplies the cooling oil in the cooling oil tank, in addition to the cooling oil from the first hydraulic pump, to the braking system and the transmission; characterised by a hydraulic motor 54 whose output axis is connected to an input axis of the second hydraulic pump; a hydraulic oil tank 24 for storing hydraulic oil; a third hydraulic pump 53 that is driven by the engine and supplies the hydraulic oil in the hydraulic oil tank to the hydraulic motor; a flow amount adjuster 55 that is provided along a bypass channel 28 that lets a predetermined amount of the hydraulic oil from the third hydraulic pump bypass the hydraulic motor and adjusts a bypass flow amount in the bypass channel; and a controller 57 that controls the bypass flow amount at the flow amount adjuster based on a brake status in the braking system, a capacity of the first hydraulic pump corresponding to a flow amount of the cooling oil required to lubricate the transmission, a capacity of the second hydraulic pump corresponding to a flow amount of the cooling oil to make up for the cooling oil from the first hydraulic pump in order to provide the cooling oil supplied when the braking system is in operation, and a capacity of the third hydraulic pump being smaller than a capacity of the second hydraulic pump.