A fixing device including a lubricant supply unit is provided. The lubricant supply unit supplies a lubricant between a fixing belt and a nip forming member and includes a lubricant storage member and an impregnation member. The lubricant storage member stores the lubricant, and the impregnation member impregnates the lubricant discharged from the lubricant storage member and supplies the lubricant to an inner surface of the fixing belt. The lubricant stored in the lubricant storage member includes base oil and a thickener, and a weight of the thickener is equal to or less than 20% with respect to a weight of the lubricant.