An image forming apparatus detecting container's dismounting. A drive unit rotates the container for replenishing toner to a development unit. An output unit outputs a first signal while a predetermined portion of the container is detected, and outputs a second signal while the predetermined portion is not detected. A decision unit decides a count of changes from the second signal to the first signal based on a toner replenishing amount. A detection unit detects dismounting of the container in a case where the first signal is changed to the second signal during not rotating. The controller stops the rotation in a case where the count of changes reaches the count decided, controls the drive unit to output the first signal in a case where containers should be exchanged, and does not control the drive unit to output the first signal in a case where containers should not be exchanged.