The present invention provides a thermoplastic polyester elastomer excellent in heat resistance, heat-aging resistance, water resistance, light resistance, low-temperature property and the like, and further excellent in block order-retaining ability, the thermoplastic polyester elastomer comprising a hard segment which comprises polyester constituted with aromatic dicarboxylic acid and aliphatic or alicyclic diol and a soft segment which comprises mainly aliphatic polycarbonate, wherein the hard segment and the soft segment being connected, and wherein when melting points of the thermoplastic polyester elastomer are obtained by measuring on a differential scanning calorimeter in three cycles in which a temperature is raised from room temperature to 300° C. at a heating rate of 20° C./min., maintained at 300° C. for 3 minutes and lowered to room temperature at a cooling rate of 100° C./min., a melting point difference (Tm1−Tm3) between a melting point obtained in the first cycle (Tm1) and a melting point obtained in the third cycle (Tm3) is 0-50° C., and a tensile strength at break is 15-100 MPa.