A haulage vehicle comprising: a vehicle frame that travels by wheels ; a vessel that is mounted tiltably on the vehicle frame and is to be loaded with a payload as an object to be hauled; hoist cylinders that are disposed telescopically between the vessel and the vehicle frame and extends to tilt the vessel with respect to the vehicle frame when ejecting the payload from the vessel; a hydraulic power source that produces pressurized oil to be supplied to the hoist cylinders ; a control valve device that is arranged between the hydraulic power source and the hoist cylinders and opens or closes a valve for supplying or discharging the pressurized oil to or from the hoist cylinders ; a controller that performs open or closure control on the control valve device ; and a tilt angle detector that detects a tilt angle of the vessel with respect to the vehicle frame ; and a speed detector that detects a travel speed of the haulage vehicle, characterized in that the controller comprises a down assist control section configured to compare a down assist performing angle, which is a tilt angle preset to determine whether negative pressure control processing needs to be performed for offsetting a force applied in a direction that would cause the hoist cylinders to extend, with the detected tilt angle and, if the detected tilt angle is determined to be equal to or greater than the down assist performing angle, to output a control valve signal to the control valve device so that the valve is opened to forcibly discharge pressurized oil from the hoist cylinders , wherein the controller is configured to output the control valve signal if the travel speed detected by the speed detector is equal to or greater than a speed threshold preset to determine a stationary state of the haulage vehicle and the tilt angle of the vessel is equal to or greater than the down assist performing angle. a vehicle frame that travels by wheels ; a vessel that is mounted tiltably on the vehicle frame and is to be loaded with a payload as an object to be hauled; hoist cylinders that are disposed telescopically between the vessel and the vehicle frame and extends to tilt the vessel with respect to the vehicle frame when ejecting the payload from the vessel; a hydraulic power source that produces pressurized oil to be supplied to the hoist cylinders ; a control valve device that is arranged between the hydraulic power source and the hoist cylinders and opens or closes a valve for supplying or discharging the pressurized oil to or from the hoist cylinders ; a controller that performs open or closure control on the control valve device ; and a tilt angle detector that detects a tilt angle of the vessel with respect to the vehicle frame ; and a speed detector that detects a travel speed of the haulage vehicle, characterized in that the controller comprises a down assist control section configured to compare a down assist performing angle, which is a tilt angle preset to determine whether negative pressure control processing needs to be performed for offsetting a force applied in a direction that would cause the hoist cylinders to extend, with the detected tilt angle and, if the detected tilt angle is determined to be equal to or greater than the down assist performing angle, to output a control valve signal to the control valve device so that the valve is opened to forcibly discharge pressurized oil from the hoist cylinders , wherein the controller is configured to output the control valve signal if the travel speed detected by the speed detector is equal to or greater than a speed threshold preset to determine a stationary state of the haulage vehicle and the tilt angle of the vessel is equal to or greater than the down assist performing angle. <EOS>