PURPOSE: To provide a device which is constituted to improve the starting device of a slide throttle valve and improve acceleration operation after deceleration operation of an engine.

CONSTITUTION: An air passage 22 for starting connected to an intake air passage 2B situated upper stream from a slide throttle valve 13 is opened to a starting valve guide cylinder 21 and an air passage 34 for idling communicated with an intake air passage 2A situated downstream from a slide throttle valve through a control valve seat 35 is branched from the air passage for starting and the control valve seat is provided with a regulation valve 36. During idling, the slide throttle valve is held in a fully closed state and air for idling is fed to a downstream intake air passage through the air passage for starting, the control valve seat, and the air passage for idling. Meanwhile, in such a state that the air passage for starting opening in the starting valve guide cylinder and an air-fuel mixture passage for starting are closed by a starting valve 28, a gap provided between a needle valve 30 for starting and a fuel nozzle 24 for starting is controlled to a microvalue and fuel draft is suppressed.