To provide technology for highly refining and uniforming the dispersed phase of a polymeric composite material which has the dispersed phase of a biomass-derived component formed in a mother phase of a synthetic high polymer.

This polymeric composite material manufacturing device 10 comprises a cylinder 13 in which a charge section A is provided at the upstream side for charging main agent of the synthetic high polymer and excessive aqueous material of the biomass derived component and in which a removing means 17 is provided at the downstream side, a screw 15 to be axially rotated in the cylinder 13 where a kneading temperature Tz is set to melt the synthetic high polymer, for pushing a kneaded material of the main agent and the excessive aqueous material toward the removing means 17, and a dewatering means 40 provided on the cylinder 13 for dewatering the kneaded material at set pressure Pa, Pb, Pc which is lower than saturated vapor pressure Pz at the kneading temperature Tz and higher than atmospheric pressure.