Image reading device, image forming apparatus and image reading system

An image reading device comprising:

• a reading part which reads an image of a document placed on a document placement face;
• a document pressing part openable and closable between a closing position where the document is pressed on the document placement face by the document pressing part and an opening position where the document is permitted to be removed from the document placement face;
• a capacitance sensor which is provided in the document pressing part and detects a capacitance varying in response to opening and closing of the document pressing part and presence or absence of the document on the document placement face;
• a controller which determines that the document pressing part is disposed in the closing position and that the document is placed on the document placement face, based on a detection result of the capacitance sensor;
• and
• an informing part which informs a user of leaving the document on the document placement face behind in a case where the controller determines that the document placement part is disposed in the closing position and the document is placed on the document placement face after a predetermined time elapses from a completion of an image reading in the reading part.