A specified transition metal compound having two transition metals and two cyclopentadiene type anion skeletons in its molecule and said metals are linked through an atom of Group XVI of the Periodic Table of the Elements, an olefin polymerization catalyst component comprising said transition metal compound, an olefin polymerization catalyst comprising said transition metal compound, a specific organoaluminum compound, and a specific boron compound, and a process for producing an olefin polymer using said olefin polymerization catalyst.