A method for amplifying genomic DNA is provided. The method comprises the steps of: (1) incubating a cell-containing agarose solution at a pH of 9 to 12 and a temperature of 45 to 80.degree. C. to produce a genomic DNA-dispersed agarose solution wherein 0.002 to 1 copies/5 microliter of single-stranded genomic DNA is dispersed; (2) solidifying the genomic DNA-dispersed agarose solution to produce a genomic DNA-dispersed agarose gel and neutralizing a pH of the gel; and (3) adding a DNA polymerase with strand displacement activity, primer and dNTP to the genomic DNA-dispersed agarose gel and incubating the gel at a temperature of 0 to 60.degree. C. to amplify the genomic DNA.