Polymerized toner and production process thereof

An image forming apparatus, comprising a photosensitive member, a means for charging the surface of the photosensitive member, a means for forming an electrostatic latent image on the surface of the photosensitive member, a means for receiving a toner, a means for supplying the toner to develop the electrostatic latent image on the surface of the photosensitive member, thereby forming a toner image, and a means for transferring the toner image from the surface of the photosensitive member to a transfer medium, wherein the means for receiving the toner contains a polymerized toner of core-shell structure, comprising core particles composed of colored polymer particles having a volume average particle diameter (dv) of 0.5-20 .mu.m and a ratio (dv/dp) of the volume average particle diameter (dv) to a number average particle diameter (dp) of at most 1.7, and shell which is formed of a polymer layer having an average film thickness of 0.001-0.1 .mu.m and covers each of the core particles, wherein a glass transition temperature of a polymer component making up the core particles is 10-60.degree. C.