To simply produce the subject complex compound useful as one component, etc., of a catalyst for polymerizing an olefin by condensing cyclopentadiene, etc., with an aliphatic aldehyde using a basic catalyst and then reacting the resultant reactional solution with a metal hydride and further a specific halide.

(A) Cyclopentadiene or an alkylcyclopentadiene is condensed with (B) an aliphatic aldehyde by using a basic catalyst. The resultant reactional solution is then reacted with (C) a metal hydride (lithium aluminum hydride, etc.) and further (D) a halide of a metal selected from among Fe, Ti, Hf and Zr. Thereby, the subject complex compound is obtained by the reactions with slight dangerousness and a small number of steps.