A fuel supply apparatus for a general purpose engine, the fuel supply apparatus comprising: a carburetor provided in an air intake line extending from an air cleaner to an air intake port of the general purpose engine; a pressure reduction connection channel connecting a float chamber of the carburetor and the air cleaner; a control valve provided in the pressure reduction connection channel, the control valve being controllable in a manner that the control valve can be fully closed, and that an opening degree of the control valve can be changed continuously; an air fuel ratio sensor configured to detect an air fuel ratio of an exhaust gas discharged from a combustion chamber of the general purpose engine; and a control unit configured to control the opening degree of the control valve based on a detection signal of the air fuel ratio sensor, characterized by a pressure reduction pump provided in the pressure reduction connection channel and configured to suck the float chamber to reduce a pressure in the float chamber; wherein the pressure reduction pump comprises a diaphragm pump operated in response to a negative pressure and a positive pressure generated alternately inside a crankcase of the general purpose engine, the pressure reduction pump includes a housing that is divided into an intake chamber, a discharge chamber, and a diaphragm chamber, a diaphragm that divides the diaphragm chamber into a pump chamber and an air chamber, the air chamber is connected to the crankcase by a connection pipe, the pressure reduction connection channel is opened to atmospheric air through an air filter, the pressure reduction connection channel connects the intake chamber and the float chamber, the discharge chamber is connected to the air intake line. a carburetor provided in an air intake line extending from an air cleaner to an air intake port of the general purpose engine; a pressure reduction connection channel connecting a float chamber of the carburetor and the air cleaner; a control valve provided in the pressure reduction connection channel, the control valve being controllable in a manner that the control valve can be fully closed, and that an opening degree of the control valve can be changed continuously; an air fuel ratio sensor configured to detect an air fuel ratio of an exhaust gas discharged from a combustion chamber of the general purpose engine; and a control unit configured to control the opening degree of the control valve based on a detection signal of the air fuel ratio sensor, characterized by a pressure reduction pump provided in the pressure reduction connection channel and configured to suck the float chamber to reduce a pressure in the float chamber; wherein the pressure reduction pump comprises a diaphragm pump operated in response to a negative pressure and a positive pressure generated alternately inside a crankcase of the general purpose engine, the pressure reduction pump includes a housing that is divided into an intake chamber, a discharge chamber, and a diaphragm chamber, a diaphragm that divides the diaphragm chamber into a pump chamber and an air chamber, the air chamber is connected to the crankcase by a connection pipe, the pressure reduction connection channel is opened to atmospheric air through an air filter, the pressure reduction connection channel connects the intake chamber and the float chamber, the discharge chamber is connected to the air intake line.