In an image forming apparatus, a liquid supply control processor controls to detect and store a difference amount corresponding to a displacement amount of a displacing member between a position detected by a first sensor and another position detected by a second sensor; measure a consumed liquid amount; start the liquid supply upon the consumed liquid amount reaching a predetermined threshold so as to supply the difference amount after the first sensor has detected the displacing member; and stop the liquid supply when the first sensor does not detect the displacing member before a preset predetermined time has passed. The control processor controls the image forming apparatus such that, when the liquid supply is performed without using the second sensor, using a first and second predetermined threshold times and the first threshold time is set longer than the second threshold time.