The present invention relates to a method of preparing a gene cluster construct including a plurality of genes encoding a multi-modular biosynthetic enzyme, the method including (A) a step of preparing a plurality of DNA fragments which are capable of reconstructing the gene cluster construct and have structures that can be ligated to each other and (B) a step of ligating the plurality of DNA fragments prepared in the step (A) to each other by mixing the plurality of DNA fragments in a solution to obtain the gene cluster construct.