An object of the present invention is to provide a novel catalyst for olefin (co)polymer production, which has high activity without using a large amount of a cocatalyst and is aimed for obtaining a particulate olefin (co)polymer. The invention relates to an olefin polymerization catalyst which comprises: a solid carrier (1) that has been brought into contact with a specific compound; and a metal catalyst component (2) that contains a transition metal compound (C) containing a transition metal M belonging to Group 9, 10, or 11 of the periodic table and has a reactive group Ra.