A soybean oil of a decreased content of polyunsaturated fatty acids is produced by hybridizing, selecting and raising a soybean mutant KK21 characterized by a gene having a sequence of base given by the sequence No. 1 of the sequence listing, a soybean mutant M23 characterized by deletion of a gene having a sequence of base given by the sequence No. 2 of the sequence listing, a soybean mutant M24 characterized by a gene having a sequence of base given by the sequence No. 3 of the sequence listing, a soybean mutant M5 characterized by a gene having a sequence of base given by the sequence No. 4 of the sequence listing, a soybean mutant J18 characterized by deletion of a gene having a sequence of base given by the sequence No. 5 of the sequence listing, and one or two kinds or more of these soybean mutants.