To inexpensively obtain a recycled polyester fiber with high whiteness even if using a recycled polyester, slight in the variations of physical properties, seldom causing color unevenness even after dyed in the form of a fabric, and suitably usable to clothing applications.

The recycled polyester fiber is obtained by adding a copolymerizable component to a low-molecular weight product that is obtained by depolymerizing a recycled polyester followed by carrying out a polymerization again. The recycled polyester fiber is characterized by being ≥30 mass% in recycled polyester content.