An image forming apparatus to form an image includes a mounting portion on which a container containing toner is mounted, a motor to rotate an agitation member in the container, an electrical circuit to acquire an output value corresponding to electrostaticcapacitance between electrodes of the container and a controller. The controller controls the motor to rotate the agitation member, controls the electrical circuit to acquire the output value, and controls to detect the amount of the toner in the container based on the acquired output value. The controller controls to write predetermined information in a memory of the container where the detected amount is below a predetermined amount. Where the predetermined information is stored in the memory of the container currently mounted on the mounting portion, the controller determines whether the container is a refilled container based on the output value acquired while the agitation member is rotating.