Agent capable of doubling rice plant nuclear chromosome, and use thereof

Disclosed is an agent for doubling a rice plant nuclear chromosome, which has a smaller influence on human bodies compared to conventional products and can be applied only to a specific tissue or cell in a rice plant.  Specifically disclosed is an agent for doubling a rice plant nuclear chromosome, which comprises at least a part of a nucleotide sequence encoding cyclin-dependent kinase B2 (CDKB2) or a nucleic acid comprising a sequence of which at least a part is complementary to the nucleotide sequence encoding CDKB2 as an active ingredient.