To provide a diaphragmatic caburetor for preventing the excessive reduction of the air/fuel ratio and the seizure of an engine by preventing a fuel adjusting needle from closing fully with a simple structure.

The needle 21 is engaged with an inner hole 27 of a cylindrical screw body 16. The length of the needle 32 projecting from the screw body 16 is adjusted so that a prescribed opening of a restriction 12 is secured by the needle 21 when the screw body 16 is inserted into the inner hole 27 in the full-closed position. Therefore, the fuel adjusting needle cannot be adjusted fully closed, so that the excessive thin state of the air/fuel ratio and the seizure of the engine are prevented.