1. A vector comprising: two first restriction enzyme recognition sequences different in nucleotide sequence both of which are recognized by a first restriction enzyme, wherein one of the first restriction enzyme recognition sequences comprises a part of a second restriction enzyme recognition sequence which is recognized by a second restriction enzyme that is different from the first restriction enzyme, and the other one of the first restriction enzyme recognition sequences does not comprise the part of the second restriction enzyme recognition sequence which is recognized by the second restriction enzyme; and a coding region of a specific protein for expressing a fusion protein which includes a protein and/or a protein domain encoded by a foreign gene and the specific protein linked to the protein and/or the protein domain, wherein the two first restriction enzyme recognition sequences different in nucleotide sequence are provided downstream of the coding region of the specific protein, one of said first restriction enzyme recognition sequences comprising the part of the second restriction enzyme recognition sequence is located proximal to the coding region of the specific protein, and the other first restriction enzyme recognition sequence not comprising said part of the second restriction enzyme recognition sequence is located distal to the coding region of the specific protein.