Disclosed herein are a sweetpotato SRD1 cDNA, a plant transformation vector carrying the same, and a transgenic plant comprising the vector. The thickening growth of storage roots of the transgenic sweetpotato prepared using the SRD1 cDNA is stimulated, increasing the number of storage roots by up to two times. Therefore, SRD1 according to the present subject matter is useful in the generation of transgenic root crops with high-numbered storage roots or early-maturing storage root plants.