In an image forming apparatus, it is determined whether a shortage amount of toner in a developing device is greater than a threshold value of 4 g or not, when the power is turned on to start operation. As a result, if the shortage amount of toner in the developing device is greater than 4 g, an agitating operation is executed to agitate toner in the developing device prior to a printing operation. If the shortage amount is smaller than 4 g, the agitating operation is not executed. Then, a printing command is received, and if the agitating operation is not performed, control of an operation of supplying toner is started with a delay of at least for the time required for the agitating operation, after the printing operation is started.