Image forming apparatus

An image forming apparatus comprising:

• a printing device configured to form an image on a sheet;
• a plurality of attachment portions to which a plurality of respective developer storing units is attachable, the plurality of developer storing units being configured to store developers of a same color, the developers being each supplied to the printing device;
• a remaining-amount sensing device configured to sense an amount of the developer remaining in each of the plurality of developer storing units attached to the plurality of attachment portions;
• a control device configured to select one target attachment portion from the plurality of attachment portions and select the new target attachment portion in a predefined order whenever a sense state of the remaining-amount sensing device for a target storing unit attached to the target attachment portion among the plurality of developer storing units changes from a developer-present state to a developer-empty state, the target attachment portion being a supply source of the developer for the printing device;
• an attachment sensing device configured to sense an attachment state in which the plurality of developer storing units is attached to the plurality of respective attachment portions;
• and
• a replacement operation sensing device configured to sense a replacement operation on any of the plurality of developer storing units in any of the plurality of attachment portions, wherein
• the control device outputs a replacement error notification to a display device in a case where an attachment sensing condition that the attachment state of the target attachment portion is sensed by the attachment sensing device is not established when the replacement operation is sensed.