A power transmission device disposable between a power source and a travel device , the power transmission device comprising: a torque converter device including a torque converter and a lock-up clutch and configured to transmit power from the power source to the travel device ; a first hydraulic pump driven by the power source ; a second hydraulic pump driven by the power source ; a first oil channel (L1) for supplying hydraulic fluid from the first hydraulic pump to the torque converter ; a second oil channel (L2) for draining hydraulic fluid from the torque converter ; a third oil channel (L3) that communicates with the first oil channel (L1) and the second oil channel (L2); a fourth oil channel (L4) for supplying hydraulic fluid from the second hydraulic pump to a hydraulic apparatus; a fifth oil channel (L5) that communicates with the fourth oil channel (L4) and an orifice ; a sixth oil channel (L6) that communicates with the fifth oil channel (L5) and an on/off valve ; a pressure control valve disposed in the second oil channel (L2) or the third oil channel (L3); a seventh oil channel (L7) that communicates with the sixth oil channel (L6) and the pressure control valve , and a controller configured to set the pressure control valve to an open state and to a closed state, the on/off valve configured to be switched by the controller between an ON-state, which is a closed state, and an OFF-state, which is an open state, wherein the controller sets the pressure control valve to the open state when the lock-up clutch is in an engaged state, wherein the controller sets the pressure control valve to the open state by setting the on/off valve to the ON-state. a torque converter device including a torque converter and a lock-up clutch and configured to transmit power from the power source to the travel device ; a first hydraulic pump driven by the power source ; a second hydraulic pump driven by the power source ; a first oil channel (L1) for supplying hydraulic fluid from the first hydraulic pump to the torque converter ; a second oil channel (L2) for draining hydraulic fluid from the torque converter ; a third oil channel (L3) that communicates with the first oil channel (L1) and the second oil channel (L2); a fourth oil channel (L4) for supplying hydraulic fluid from the second hydraulic pump to a hydraulic apparatus; a fifth oil channel (L5) that communicates with the fourth oil channel (L4) and an orifice ; a sixth oil channel (L6) that communicates with the fifth oil channel (L5) and an on/off valve ; a pressure control valve disposed in the second oil channel (L2) or the third oil channel (L3); a seventh oil channel (L7) that communicates with the sixth oil channel (L6) and the pressure control valve , and a controller configured to set the pressure control valve to an open state and to a closed state, the on/off valve configured to be switched by the controller between an ON-state, which is a closed state, and an OFF-state, which is an open state, wherein the controller sets the pressure control valve to the open state when the lock-up clutch is in an engaged state, wherein the controller sets the pressure control valve to the open state by setting the on/off valve to the ON-state. <EOS>