Thermoplastic polymer composition

A thermoplastic polymer composition having excellent resistance to heat discoloration has been desired. There is provided a thermoplastic polymer composition characterized by comprising a thermoplastic polymer, phosphites represented by the formula (I), and at least one kind of erythritols selected from the group consisting of pentaerythritol, dipentaerythritol and tripentaerythritol: wherein R 1 , R 2 , R 4 and R 5 each independently denotes a hydrogen atom, an alkyl group or the like, and R 3 denotes a hydrogen atom or an alkyl group; X denotes a single bound, a sulfur atom or a -CHR 6 group (R 6 denotes a hydrogen atom, an alkyl group or a cycloalkyl group); A denotes an alkylene group or a *-COR 7 group (R 7 denotes a single bond or an alkylene group, and * denotes a bonding hand on the side of oxygen), and one of Y and Z denotes a hydroxyl group or the like, and the other one of Y and Z denotes a hydrogen atom or an alkyl group).