An object of the present invention is to expand CD34+ cells
ex vivo efficiently in a short term using a biologically safe and inexpensively obtainable low molecular weight compound. A still another object of the present invention is to provide an expansion agent for CD34+ cells useful for treatment of various hematopoietic disorders caused by dysfunctional hematopoietic stem cells and / or
hematopoietic progenitor cells.A method for expanding CD34+ cells, which comprises culturing CD34+ cells
ex vivo in the presence of a compound represented by the formula (I) (wherein A, B, L1, L2, L3, L4, R1, R2, R3, X and Y are defined in the description), a
tautomer or pharmaceutically acceptable salt of the compound or a solvate thereof.