A parting agent for a copier toner is disclosed. The parting agent exhibits no loss of parting properties or generation of gel under high-temperature conditions near 200° C., and causes no problems with paper feed or the like. The parting agent is composed of a diorganopolysiloxane of the average unit formula: RaSiO4−a/2, where the R groups are the same or different and are substituted or unsubstituted monovalent hydrocarbon groups, with at least 50 mol % of the R groups being methyl groups, and 1.95 ≦a≦2.20. The diorganopolysiloxane has a viscosity of 10 to 100,000 centistokes at 25° C., and generates no more than 5 ppm (by weight) of formaldehyde per hour when kept at 200° C. in an air atmosphere.