To provide an opening/closing detecting mechanism for the opening/closing member of an interchangeable unit with which the damage of an image forming apparatus main body can be prevented without making cost high, and an image forming apparatus using the mechanism.

The interchangeable unit 1 has a photoreceptor 2 and the opening/closing member 3, and an ID chip 4 is mounted on the member 3. The member 3 is provided to protect the photoreceptor 2. The image forming apparatus 10 is equipped with a main body side ID chip I/F part 15 being an interface with the ID chip 4. In the unit 1, the other part of the member 3 is covered with a case. When attaching the unit 1 in the apparatus 10, the member 3 gets in an open state from a closed state and the photoreceptor 2 is exposed, so that the photoreceptor 2 comes into contact with the inside of the main body of the apparatus 10. When the member 3 is in the open state, the ID chip 4 is electrically connected to the ID chip I/F part 15 provided in the apparatus 10 so as to detect the open state of the member 3.