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 for supplying hydraulic fluid from the first hydraulic pump to the torque converter; a second oil channel for draining hydraulic fluid from the torque converter; a third oil channel that communicates with the first oil channel and the second oil channel; a fourth oil channel for supplying hydraulic fluid from the second hydraulic pump to a hydraulic apparatus; a fifth oil channel that communicates with the fourth oil channel and an orifice; a sixth oil channel that communicates with the fifth oil channel and an on/off valve; a pressure control valve (32, 33, 36) disposed in the second oil channel or the third oil channel; a seventh oil channel that communicates with the sixth oil channel and the pressure control valve (32, 33, 36), and a controller configured to set the pressure control valve (32, 33, 36) 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 (32, 33, 36) to the open state when the lock-up clutch is in an engaged state, wherein the controller sets the pressure control valve (32, 33, 36) 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 for supplying hydraulic fluid from the first hydraulic pump to the torque converter; a second oil channel for draining hydraulic fluid from the torque converter; a third oil channel that communicates with the first oil channel and the second oil channel; a fourth oil channel for supplying hydraulic fluid from the second hydraulic pump to a hydraulic apparatus; a fifth oil channel that communicates with the fourth oil channel and an orifice; a sixth oil channel that communicates with the fifth oil channel and an on/off valve; a pressure control valve (32, 33, 36) disposed in the second oil channel or the third oil channel; a seventh oil channel that communicates with the sixth oil channel and the pressure control valve (32, 33, 36), and a controller configured to set the pressure control valve (32, 33, 36) 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 (32, 33, 36) to the open state when the lock-up clutch is in an engaged state, wherein the controller sets the pressure control valve (32, 33, 36) to the open state by setting the on/off valve to the ON-state.