A lubricant supplying device includes a lubricant supplying roller configured to rotate in a certain direction and makes a sliding contact with an image carrier on which a toner image is carried; a solid lubricant arranged to slide in contact with the lubricant supplying roller; a changing unit configured to change a revolution of the lubricant supplying roller to adjust an amount of the solid lubricant supplied onto the image carrier; and a calculation unit configured to obtain a product life or total consumption of the solid lubricant from a total running distance or total operating time of the image carrier or the lubricant supplying roller, the product life or the total consumption of the solid lubricant being corrected based on the amount of the solid lubricant supplied onto the image carrier.