Abstract: Fuel economy of a multi-cylinder internal combustion engine has been improved by allowing, when a vehicle is at a standstill, the engine to run on selected cylinders of all. The idling operation of the engine on the selected cylinders has been made smooth by the provision of a switch valve in a control circuit of the transmission. With the switch valve, as soon as an accelerator pedal is released when the vehicle is at a standstill, hydraulic fluid will be drained from the control circuit to render a gearing of the transmission in a neutral condition even if a manually selector valve in the control circuit is held in a drive range position. This prevents transmission of load to the engine through the hydrokinetic unit which otherwise would occur when the manually selector valve is in the drive range position.