(wherein R3 is a methyl group). [0022] (7) A poly(imidazolylporphyrin metal complex) having a mercapto group at both ends thereof, which is represented by a general formula (3): [0023] wherein each of R1, M, R2, X and Im including R3 has the same meaning as defined in item (1) above; and n represents an integer of 0 or more. [0024] (8) The poly(imidazolylporphyrin metal complex) represented by th