It is found that a SVVYGLR peptide (SEQ ID NO: 1) can promote proliferation of mesenchymal cells such as marrow-derived mesenchymal stem cells and dental pulp cells. A carbonate apatite-collagen sponge containing the SVVYGLR peptide (SEQ ID NO: 1) is useful as a biomaterial for the regeneration of bone marrow or dental pulp. It becomes possible to provide a skeletal system biomaterial which is capable of promoting the proliferation of the mesenchymal cells and is useful as artificial bone marrow or artificial dental pulp for repairing a defect in a bone marrow tissue or a dental pulp tissue.