The present invention provides a fusion protein which delivers a functional protein or peptide into a cell at enhanced efficiency. The fusion protein of the present invention is a transduction domain-target protein-transduction domain fusion protein, wherein the transduction domain, which comprises 6-12 amino acid residues whose more than 3/4 consist of arginine or lysine residues, is covalently bonded to each of the amino- and carboxyl-terminal ends of the target protein. Green fluorescence protein and Cu/Zn-superoxide dismutate (SOD) are used as the target protein.