To attain lubricating performance as required by quickly increasing the temperature of operating oil during cold.

A cover 84 is integrally provided for wholly covering a housing 80 of a torque converter 12 using operating oil common with a lubricating oil for an automatic transmission to form an approximately vacuum closed space 82 which serves for heat insulating effects as required. The temperature of the operating oil is, therefore, quickly increased with heat generated by the rotation, stirring and friction of the operating oil accompanying the rotation of a pump impeller 20. Accordingly, even at initially starting the operation of a vehicle during cold, for example, bellow the freezing point, the temperature of the operating oil is increased by the torque converter 12 quickly after starting the operation, attaining quick lubricating performance as required and improving the worsening of fuel economy resulting from an increase in friction with an increase in viscosity.