To communicate an air passage from a fuel tank with an intake port of outside air by a cylindrical part being a fuel passage of a bistarter when operating the bistarter at cold starting time of an engine.

In this diaphragm type carburetor for opening the fuel passage 32 from a constant pressure fuel chamber 25 of this carburetor in a downstream side part more than a throttle valve 47 of an intake air passage 16 via a check valve 33 and the cylindrical part 40 of the bistarter 20, the carburetor is provided with a valve element 41 for switching a position to a position for connecting the air passage 44 from the fuel tank 46 and an intake port 39 of the outside air to the cylindrical part 40 of the bistarter 20 and a position for cutting off the fuel passage 32, the air passage 44 and the intake port 39 from the cylindrical part 40.