Disclosed is an amplifier for hematopoietic stem cells and/or hematopoietic progenitor cells which is useful for treating various diseases and for improving the efficiency of transferring a gene into hematopoietic stem cells in gene therapy.An amplifier for hematopoietic stem cells and/or hematopoietic progenitor cells and a drug, which contain, as the active ingredient, a compound represented by formula (I) [wherein X, Y, Z, Ar