PROBLEM TO BE SOLVED: To provide an agent which controls transposon transfer.SOLUTION: The invention is a transposon transfer inhibitor containing Ganoderma lucidum extract. Using Ganoderma lucidum extract of the invention promotes production of a DNA methylation enzyme specific to a transposon, thereby transposon transfer can be controlled. And using Ganoderma lucidum extract of the invention can prevent or alleviate diseases caused by transposon transfer, such as muscular dystrophy, hemophilia, Alzheimers disease, and malignant tumor.