A fixing device includes a pair of detachable rollers and applies heat and pressure to a sheet nipped between the rollers to fix a toner image formed on the sheet to the sheet. The fixing device includes a biasing part which gives a biasing force to bring one of the rollers into tight contact with the other, an adjusting part which adjusts the biasing force of the biasing part, and a guide indication part providing a guide for an amount of adjustment to be made by the adjusting part in accordance with the hardness of the surface layer of a roller of the rollers.