A liquid developer contains an insulation liquid containing as its main component a glyceride of an unsaturated fatty acid, toner particles dispersed in the insulation liquid; and an oxidation polymerization accelerator for accelerating oxidation polymerization reaction of the glyceride during fixing process of the toner particles. The oxidation polymerization accelerator accelerates the oxidation polymerization reaction by supplying oxygen during the fixing process of the toner particles. The liquid developer may further contain an antioxidizing agent. Preferably, the oxidation polymerization accelerator is contained in the insulation liquid being encapsulated.