According to one embodiment, a developing agent includes a toner resin containing a coloring material, a binder resin, an ester wax and a crystalline polyester resin. The ester wax has an alkyl group with a carbon number of from 32 to 46, when an ion intensity ratio at each carbon number is expressed in terms of percentage, a content of an ester compound having a carbon number showing its maximum intensity ratio is from 20 to 55% by weight of the whole of the wax, and a content of ester compounds with a carbon number of not more than 38 is not more than 10% by weight of the whole of the wax. The ester wax has an endothermic peak measured by DSC of from 60 to 75° C. The crystalline polyester resin has an endothermic peak measured by DSC of from 90 to 110° C.