A torque converter having a lockup mechanism makes it possible to positively and forcibly suppress the frictional heat and others generated on the frictional surfaces of the lockup clutch and its counterpart while the lockup clutch is in operation, particularly in a slipping state. Hence, the life of the lockup clutch or that of the torque converter as a whole is prolonged. In this torque converter having the lockup mechanism, a hydraulic control mechanism is provided for maintaining the difference of pressure substantially at a constant level and changing the flow rate of a fluid to be supplied to the frictional surface of the lockup clutch in order to control the slipping state of the lockup clutch. Oil grooves are cut on the frictional member of the lockup clutch.