PROBLEM TO BE SOLVED: To provide a mutant in which a starch synthase type I (SSI) gene of rice is knocked out, a method to elucidate SSI function by the mutant, a new starch and provide a method for producing the starch. SOLUTION: In the mutant, a transposon is inserted into the starch synthase type I gene and the starch synthase type I gene is knocked out. In the method for producing the mutant, the starch synthase type I gene is knocked out comprising introducing an activated retrotransposon into a genome of rice, inserting the transposon into a position of the starch synthase type I gene and selecting the inserted gene. Further, the new starch having physical properties different from wild type produced from the mutant and the method for producing the starch are provided.
