A mechanism for mixing a supercritical fluid and a polymer raw material melt provided by the present invention includes a hot-melting unit, a mixing unit, and a supercritical fluid supplying unit. The mixing unit, independently of the hot-melting unit, receives a polymer melt from the hot-melting unit and a supercritical fluid from the supercritical fluid supplying unit, respectively, and mixes the polymer melt and the supercritical fluid into a homogenous single-phase solution. The hot-melting unit is provided with a pushing member for pushing a polymer raw material. The mixing unit is provided with a mixing rotor for mixing the polymer melt and the supercritical fluid.