Image forming apparatus

An image forming apparatus comprising:

• a developing unit including (I) an accommodation portion configured to accommodate a developer, (II) a developing member configured to develop an electrostatic latent image formed on a photosensitive drum with the developer accommodated in the accommodation portion, and (III) a magnetic body unit including a magnetic body, the magnetic body unit being located inside the accommodation portion and supported to be movable relative to the accommodation portion in a moving direction;
• a rotary configured to rotate, the rotary including the developing unit;
• and
• a magnetic sensor,
• wherein a rotation period for the rotary to make one rotation includes a first period,
• wherein in the first period, the moving direction includes a vertically downward component,
• wherein the first period includes a contact period during which the magnetic body unit contacts the developer and is received by the developer,
• wherein the contact period includes parallel timing at which a rotation center of the rotary, the magnetic body unit, and the magnetic sensor are aligned on a straight line in a radial direction of rotation of the rotary as viewed in a rotation axis direction of the rotary, and
• wherein the magnetic sensor is configured to output a signal based on a magnetic field produced by the magnetic body in at least a part of the first period.