The present invention provides a highly economical process for production of an inorganic filler-containing polyolefin resin composition, and a production apparatus to be used for the process, whose process is characterized by carrying out a continuous series of steps from an olefin polymerization step up to a kneading/pelletizing step wherein the polyolefin resin obtained by the polymerization step is kneaded and pelletized with an inorganic filler and various additives.