An image forming apparatus comprising: an image forming unit attachable to or detachable from a predetermined position; a rotation force transmission mechanism configured to transmit a rotation force from a driving source to the image forming unit; a manual lever configured to switch the rotation force transmission mechanism into a transmission state in which the rotation force transmission mechanism is coupled to the image forming unit and a transmission release state in which the rotation force transmission mechanism is spaced away from the image forming unit; and characterized in that the image forming apparatus further comprising: an incorrect attachment or detachment preventing mechanism configured to prevent attachment and detachment of the image forming unit in the transmission state, wherein the incorrect attachment and detachment preventing mechanism includes a locking member capable of moving to a restrict position where the locking member restricts movement of the image forming unit from the predetermined position and a permission position where the locking member permits movement of the image forming unit from the predetermined position, the manual lever is formed with a first engaging part configured to engage with the locking member at the restrict position and a second engaging part configured to engage with the locking member at the permission state; and when the manual lever switches the rotation force transmission mechanism into the transmission state, the locking member is configured to engage with the first engaging part of the manual lever at the restrict position to prevent movement of the image forming unit, and when the manual lever switches the rotation force transmission mechanism into the transmission release state, the locking member is configured to be moved to the permission position and then engaged with the second engaging part of the manual lever to permit movement of the image forming unit. an image forming unit attachable to or detachable from a predetermined position; a rotation force transmission mechanism configured to transmit a rotation force from a driving source to the image forming unit; a manual lever configured to switch the rotation force transmission mechanism into a transmission state in which the rotation force transmission mechanism is coupled to the image forming unit and a transmission release state in which the rotation force transmission mechanism is spaced away from the image forming unit; and an incorrect attachment or detachment preventing mechanism configured to prevent attachment and detachment of the image forming unit in the transmission state, wherein the incorrect attachment and detachment preventing mechanism includes a locking member capable of moving to a restrict position where the locking member restricts movement of the image forming unit from the predetermined position and a permission position where the locking member permits movement of the image forming unit from the predetermined position, the manual lever is formed with a first engaging part configured to engage with the locking member at the restrict position and a second engaging part configured to engage with the locking member at the permission state; and when the manual lever switches the rotation force transmission mechanism into the transmission state, the locking member is configured to engage with the first engaging part of the manual lever at the restrict position to prevent movement of the image forming unit, and when the manual lever switches the rotation force transmission mechanism into the transmission release state, the locking member is configured to be moved to the permission position and then engaged with the second engaging part of the manual lever to permit movement of the image forming unit.