To surely and easily perform low temperature starting of an engine with a small number of crankings by enbling properly supplying of starting fuel for a general engine without skill.

An upstream side and a downstream side of a throttle valve on an intake passage is connected to each other through a bypass 31, while a constant fuel chamber 12 is connected with the bypass 31 by means of an increasing fuel passage 32 provided with a check valve 33. The bypass 31 and the increasing fuel passage 32 are opened and closed substantially at the same time by means of a manually operated valve 40. A required amount of starting fuel is supplied to an engine for a short time through the increasing fuel passage 32 to start the engine with a small number of crankings. Idling malfunction and discharge operation of inflow air are eliminated by preventing inflow of air into the constant fuel chamber 12 through the check valve 33. Starting operation can be done at random for unnecessitating skill of an operator.