Mouse PCLP1 was identified by expression cloning with the use of a monoclonal antibody against a surface antigen of a cell line derived from mouse AGM. By fractionating PCLP1-positive/CD45-negative cells and culturing them in vitro, it was clarified that these cells differentiate into endothelial-like cells, angioblast-like cells, and hematopoietic cells. By transferring the PCLP1-positive/CD45-negative cells into a mouse defective in the hematopoietic function, the hematopoietic system was reconstructed over a long period of time. These facts indicate that the PCLP1-positive/CD45-negative cells contain mammalian hemangioblasts capable of expressing the activity as long-term repopulating hematopoietic stem cells (LTR-HSC). The present invention provides a method for preparing a cell fraction containing hemangioblasts, the cell fraction prepared by the method, and use of this cell fraction.