A lock-up control device controls a lock-up clutch in a torque converter. The lock-up clutch is engaged by supplying a lock-up control pressure. The torque converter transmits torque via oil in a torque converter chamber when the lock-up clutch is disengaged, and transmits torque directly when the lock-up clutch is engaged. In the lock-up state, the oil pressure in the torque converter chamber is decreased by discharging oil in the torque converter chamber. By providing a circuit which leads oil discharged from the torque converter chamber to a lubricating part of the transmission, the balance between the inflowing oil amount and outflowing oil amount is improved, and oil insufficiency is prevented.