We investigated the electronic properties of Fe tape-porphyrin and the effect of CO adsorption on it within the framework of density functional theory. As for the numerical results, we found that the Fe tape-porphyrin is metallic, and that the CO-adsorbed Fe tape-porphyrin is an insulator. Comparing the electronic structures of the Fe porphyrin molecule and the CO-adsorbed one, we found that the metal-insulator transition is caused by the hybridization of the d(xz) and d(yz) orbitals of Fe with the π(g)(*) orbital of CO.