A toner supply device which includes: a multiple number of toner bottles; and a toner supply assembly mounting mechanism having the toner bottles mounted thereon and feeding toner discharged from the toner bottles to a developing unit and is controlled so as to supply toner to the developing unit in accordance with the amount of toner consumed in the process of printing of the developing unit, further includes: micro switches which each detect the amount of toner left in the toner storing portion with toner filled therein; and a controller for controlling the operation of the toner supply device, which selects one of the toner bottles to be used for supply of toner to a toner feed device, based on the amounts of toner in the multiple toner bottles, which are detected by the micro switches.