To obtain an antistatic agent causing no crack in the polyester as sheath component due to a post-processing such as alkali reduction even in case of being continuously charged in a long striated manner in polyester fibers, thus capable of exerting sufficient antistatic performance.

A polyester composition with a relative viscosity of 2.8 or higher is provided, being such that 50-85 wt.% of a polyalkylene glycol 10,000 or higher in weight-average molecular weight and 10-40 wt.% of an organic metal sulfonate compound of the chemical formula 1 are compounded with each other so as to meet the relationship 1 the below, and the rest of the component consists of a polyester component. The chemical formula 1 is as follows: RSO3M (wherein, R is a 6C alkyl, aryl or alkylaryl; and M is an alkali metal or alkaline earth metal atom). The relationship 1 is as follows: 80(wt.%)(A+B)95(wt.%) (wherein, A denotes the amount of a polyalkylene glycol component; and B denotes the amount of an organic metal sulfonate compound component).