Thermoplastic polyester elastomer, resin composition containing same, and molded article obtained therefrom

Provided is a thermoplastic polyester elastomer which, in particular, has excellent extrusion moldability and extrusion molding stability, and which enables the production of a hollow and long molded article by extrusion molding at a uniform thickness stably over a long period of time. A polyester elastomer obtained by bonding a hard segment comprising a polyester composed of an aromatic dicarboxylic acid and an aliphatic or cycloaliphatic diol and a soft segment comprising an aliphatic polycarbonate, at least some of the terminal groups of the polyester elastomer being terminated with a reactive compound, the reactive compound contains a polycarbodiimide, the acid value of the polyester elastomer is 15 eq/ton or less, and under the condition of 230 DEG C, (i) the melt viscosity at a preheating time of 5 minutes and a shear rate of 10/sec is 1800 Pa.s or more, and the melt viscosity at a preheating time of 5 minutes and a shear rate of 1000/sec is 800 Pa.s or less; and (ii) the melt viscosity ratio at a shear