A method of culturing Lin−negative or weakly positive cells characterized by culturing in the presence of macrophage colony stimulating factor (M−CSF); a method of amplifying hematopoietic stem cells characterized by culturing Lin−negative or weakly positive cells in the presence of M−CSF; a hematopoietic stem cell mass obtained by the amplification method; a kit for culturing Lin−negative or weakly positive cells containing M−CSF; and a hematopoietic stem cell amplification promoter containing M−CSF.
