A toner remain detecting method according to this invention including: detecting toner density; supplying a toner amount corresponding to predetermined toner density; detecting a toner remain amount every time toner supply is carried out; and displaying toner near-empty if the toner remain amount becomes equal to or less than a prescribed value; wherein the toner supply step includes calculating a toner supply amount on the basis of a predetermined toner density level and the toner remain amount detected at the toner remain amount detecting step and supplying toner of the amount calculated at the toner supply amount calculating step. With the toner remain detecting method according to this invention, the toner remain amount can be detected more accurately than in conventional techniques.