Abstract: It is intended to provide a process for industrially safely and/or economically and efficiently producing a polyester by using gene manipulation techniques. A vector applicable to hosts over a wide range which is characterized by having improved industrial safety; a polyester synthase-expressing plasmid wherein at least a polyester synthase gene is transferred into said vector; a transformant capable of synthesizing a polyester which contains the plasmid; and a process for producing a polyester with the use of the plasmid or the transformant.