To provide a charge retention medium having a surface potential at a practical level, although it is obtained from a composition containing a fluorinated copolymer having repeating units based on tetrafluoroethylene and repeating units based on ethylene. A charge retention medium (electret 30) which is obtained from a composition containing a fluorinated copolymer (A) having repeating units based on tetrafluoroethylene and repeating units based on ethylene; and at least one charge aid (B) selected from the group consisting of a compound having at least one amino group and at least one reactive functional group (excluding an amino group) and a compound having at least two amino groups and having no reactive functional group (excluding an amino group).
