Image reading device and image forming system

An image reading device comprising:

• a transparent document table on which a document is placed;
• a frame provided around a peripheral of the document table;
• a reading unit which reads the document in a main scanning direction;
• a moving mechanism which moves the reading unit in a sub scanning direction crossing to the main scanning direction;
• a white reference member provided on the frame adjacent to the document table in the sub scanning direction and having a length in the main scanning direction longer than the document table;
• and
• a controller which controls the moving mechanism, wherein
• the reading unit includes a first reading part which reads an area corresponding to the document table and a second reading part which reads an area corresponding to the frame, and
• the controller detects a boundary between the frame and the reference member based on a read value of the second reading part while moving the reading unit by the moving mechanism, and positions the reading unit at a home position apart from the boundary by a predetermined distance.