PURPOSE: To quickly start an engine by ordinary operation even in the case of lowering of the oil level in a carburetor float chamber.

CONSTITUTION: In a negative pressure type fuel cock 1 provided with a rod 10 by which a fuel flow passage is closed by means of a spring 14 in a negative pressure chamber 11 at stopping an engine, and the flow passage is opened by the negative pressure of the engine transmitted to a negative pressure chamber at operating the engine, a camshaft 18 to move the rod 10 in the direction of opening the flow passage interlocking with the operation of a cab--starter is insertedly provided, and hence fuel is supplied into a float chamber by operating the cab-starter.