A method of expanding hematopoietic stem cells and / or hematopoietic progenitor cells, wherein hematopoietic stem cells and / or hematopoietic progenitor cells to be expanded are selected from CD34 + CD38- cells, HPP-CFU colony forming cells or SCID repopulating cells (SRC), the method of which involves adding at least one stimulating factor to a blood cell selected from the group consisting of stem cell factor (SCF), interleukin 3 (IL-3), interleukin 6 (IL -6), interleukin 11 (IL-11), flk2 / flt3 ligand (FL), granulocyte colony stimulating factor (G-CSF), granulocyte and macrophage colony stimulating factor (GM-CSF), thrombopoietin (TPO) and erythropoietin (EPO), and comprising culturing hematopoietic stem cells and / or hematopoietic progenitor cells ex vivo in the presence of a compound represented by formula (I), a pharmaceutically acceptable tautomer or salt of the compu this or a solvate thereof to proliferate hematopoietic stem cells and / or hematopoietic progenitor cells with minimal differentiation: ** Formula ** wherein each of R1 R2, R3, and R4 independently signifies a hydrogen atom or an alkyl group C1-C10, whose C1-C10 alkyl group may be linear, branched, or a C3-C10 cycloalkyl group, wherein the C1-C10 alkyl group may optionally be substituted with one or more halogen atoms, R5 signifies (a) a group C2-C14 aryl, which can be a C6-C14 aryl group that does not contain heteroatoms such as ring constituting atoms, a C2-C9 aromatic heterocyclic group or a C2-C14 fused polycyclic group, and a C2-C9 aromatic heterocyclic group can be a 5- to 7-membered C2-C6 heteromonocyclic group or an 8 to 10-membered C5-C9 fused heterobicyclic group containing 1 to 3 oxygen atoms, nitrogen atoms, or sulfur atoms, alone or in combination, wherein theC2-C14 aryl group is substituted with -V1 and, when it is a nitrogen-containing C2-C14 aryl group, it can be one of its N-oxides, (b) a hydrogen atom or a (c) C1-C6 alkyl group , whose C1-C6 alkyl group may be linear, branche
