PURPOSE: To improve saving of fuel consumption, by providing a branch pipe in the half way of a fuel intake pipe, providing one solenoid valve between the branch pipe and an outside air supply port, providing the other solenoid valve between a branching point of the branch pipe and a throttle valve and interrupting supply of fuel at running of inertial movement.

CONSTITUTION: A fuel intake pipe 11 connects a carburetor, provided with a throttle valve 8, to an intake port 10 of an engine cylinder. A solenoid valve 15 is provided between a branch pipe 13 and outside air supply pipe 14, while a solenoid valve 12, opening and closing the fuel intake pipe 11, is provided. When depressive force of an accelerator pedal is released, the solenoid valve 12 is closed while the solenoid valve 15 is opened. In this way, supply of fuel to a cylinder 9 is interrupted, and fuel can be saved.