This method for producing a template DNA comprises: step (a) for preparing a cassette double-stranded DNA; step (b) for preparing an oligonucleotide containing a target sequence; step (c) for ligating the same by a DNA ligase to thereby obtain a cyclic nucleotide containing the target sequence; step (d) for, using the nucleotide as a template, amplifying by a strand displacement DNA polymerase to thereby obtain a double-stranded DNA containing the target sequence that is a concatemer having the same sequences consisting of a support sequence, an RNA polymerase promoter sequence, the target sequence and an sgRNA scaffold sequence; and step (e) for cleaving the double-stranded DNA between the same sequences to thereby obtain a template DNA having sequences consisting of the support sequence, the RNA polymerase promoter sequence, the target sequence and the sgRNA scaffold sequence.