Image forming apparatus that performs developer replenishment

An image forming apparatus comprising:

• an image forming section including a photosensitive member, an exposure unit configured to expose said photosensitive member based on image data to form an electrostatic latent image, and a developing unit configured to contain developer having toner and develop the electrostatic latent image using the toner;
• a supply unit including a motor and configured to drive the motor based on a drive signal to supply toner from a container containing toner to said developing unit;
• a measurement unit configured to measure first information corresponding to a ratio of the toner in said developing unit to the developer in said developing unit;
• an obtaining unit configured to obtain, based on the image data, second information corresponding to an amount of the toner consumed from said developing unit;
• a controller configured to control whether or not to output the drive signal, based on the first information measured by said measurement unit and the second information obtained by said obtaining unit;
• an estimation unit configured to estimate, according to output of the drive signal from said controller, an error of a replenishment amount of the toner supplied from the container to said developing unit, based on the first information measured by said measurement unit and the second information obtained by said obtaining unit;
• and
• a determination unit configured to determine, based on the error estimated by said estimation unit, whether or not it is necessary to perform replacement of the container.