A hydraulic circuit for a power transmission device has an oil passage supplying hydraulic pressure of hydraulic fluid to the power transmission device mounted on a vehicle and a hydraulic actuator on which the hydraulic pressure of the hydraulic fluid in the oil passage acts, the oil passage is provided with a concave portion of the inner surface of the oil passage that is recessed upward in the state of mounting on the vehicle. The concave portion is located upstream of the hydraulic actuating portion in the oil passage and above the hydraulic actuating portion when the unit is mounted in the vehicle.