To provide a gaseous fuel supplying valve allowing an engine to exert its full performance, capable of simplification of the seat structure, and enhancing the seat responsiveness when the valve is to be opened and closed.

The gaseous fuel supplying valve is equipped with a nozzle 1 to supply a gaseous fuel to a suction manifold M2, a retainer 2 confronting the nozzle in the direction of valve stem (m), and a seat 3 interposed between the nozzle and retainer movably in the direction of valve stem and contacting with and separating from the nozzle. The retainer is furnished with a lead-in passage 22 to lead via the seat the gaseous fuel from a gas supply manifold M1 to the nozzle side face 3a of the seat. On the inside and outside of the seat on a circle concentrical to the valve stem, a plurality of open holes 32 and 33 penetrating in the valve stem direction so that the lead-in passage in the retainer is open in the nozzle side face of the seat are provided in such a way as continuously and having a longer diameter in the circumferential direction. On the seat inside and outside of the nozzle side face mating with the open holes, ring-shaped grooves 34 and 35 are provided recessed on a circle concentrical to the valve stem and put in communications to the open holes.