A toner conveying means disposed in a housing includes an upstream-side toner conveying means and a downstream-side toner conveying means. A toner amount detector means is disposed to detect whether the amount of toner in the downstream portion of the housing is greater than a predetermined amount or not, and the upstream-side toner conveying means is not operated when the amount of toner is greater than the predetermined amount in the downstream portion of the housing. A toner replenishment signal is produced when the amount of toner does not become greater than the predetermined amount in the downstream portion of the housing despite the downstream-side toner conveying means is operated for more than a predetermined period of time.
