The present invention provides a highly active process for producing an olefin polymer, comprising: the step (I) of preliminarily polymerizing an olefin at 65° C. or lower in the presence of a preliminary polymerization catalyst prepared by bringing the following components (A), (B) and (C) into contact with each other, to produce a preliminary polymerization catalyst component (X); and the step (II) of polymerizing an olefin in the presence of a polymerization catalyst prepared by bringing the preliminary polymerization catalyst component (X) into contact with the following component (D), to produce an olefin polymer; component (A): a metallocene-base complex, component (B): a solid co-catalyst component in which a compound capable of ionizing the metallocene-base complex into an ionic complex is supported on fine particle support, component (C): an organoaluminum compound represented by the general formula R13Al (wherein, R1 is a linear hydrocarbon group of 1 to 8 carbon atoms, wherein the R1 can be the same or different), and component (D): an organoaluminum compound represented by the general formula R23Al (wherein, R2 is a branched hydrocarbon group of 3 to 8 carbon atoms, wherein the R2 can be the same or different).