The present invention provides a reversibly immortalized mammalian liver cell line, especially CYNK-1 (deposited with International Patent Organism Depository, National Institute of Advanced Industrial Science and Technology, address: AIST Tsukuba Central 6, 1-1, Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken, 305-8566 Japan, deposited date: Mar. 10, 2004, accession number: FERM BP-08657) comprising an immortalizing gene interposed between a pair of site-specific recombination sequences and a suicide gene in the outside of the pair of site-specific recombination sequences, characterized in that the suicide gene can exhibit its function after excision of the pair of site-specific recombination sequences, or passage cell line thereof; a mammalian liver cell obtained by excising the immortalizing gene from the reversibly immortalized mammalian liver cell line or passage cell line thereof; and use of these cells. By utilizing the reversibly immortalized mammalian liver cell line of the present invention enables the obtainment of the number of the liver cells and utilization as materials for artificial liver reactors and cell preparations.