An agent for amplifying hematopoietic stem cells and/or hematopoietic progenitorcells which is useful as a method for treating various hematopoietic diseasesand is useful for improving efficiency of gene transfer to hematopoietic stemcells in gene therapy is provided. A method for amplifying hematopoietic stemcells and/or hematopoietic progenitor cells characterized by culturing hematopoieticstem cells and/or hematopoietic progenitor cells in vitro in the presence ofa compound represented by the formula (I) (wherein X, Y, Z, Ar
