PURPOSE: To smoothly start an engine by obtaining a starting mixed gas amount based on an electric signal and the atmosphere temperature at the time of manually starting its operation and the lapse of time after the engine is stopped and supplying a specified amount of starting mixed gas to the engine by means of a solenoid opening/closing valve.

CONSTITUTION: A carburetor main body 27 is provided with the passage of a bystarter E for generating thick starting mixed gas from air introduced through a part more upstream than the throttle valve 30 of an intake passage 38 and fuel introduced from a constant pressure fuel chamber 74 and supplying the mixed gas to a part more downstream than the throttle valve 30 of the intake passage 38. A solenoid opening/closing valve C for opening/closing the passage of the bystarter is controlled based on an output signal from the primary oil 9 of a flywheel magnet 7. When an engine is started, the open time of the solenoid opening/closing valve C is controlled according to the atmosphere temperature and the lapse of time after the engine is stopped.