A gas delivery system supplying a body cavity with a given gas includes a first guide pipe for supplying the given gas into the body cavity and a second guide pipe installed in the first guide pipe for supplying the given gas into the body cavity at a flow velocity that differs from that of the first guide pipe. A flow velocity of the given gas that is supplied from a first conduit which is formed by the first guide pipe and the second guide pipe is faster than a flow velocity of the given gas that is supplied from a second conduit which is formed in the second guide pipe.
