The present invention provides a prenyl diphosphate synthetase and a gene coding for the synthetase. The invention discloses a recombinant protein having the amino acid sequence shown in SEQ ID NO:2 or a recombinant protein which has the amino acid sequence shown in SEQ ID NO:2 having deletion, substitution or addition of at least one amino acid and which has decaprenyl diphosphate synthetase activity; a gene coding for the protein; a recombinant vector comprising the gene; a transformant transformed with the vector; a method for producing a decaprenyl diphosphate synthetase; and a method for producing ubiquinone-10.