An image reading device comprising: a document placing portion; a conveyor; and a reading unit configured to read an image of the document. The reading unit includes: an image sensor; and a support which supports the image sensor, wherein in the case of reading the image of the document conveyed by the conveyor. The support is to be stopped at a predetermined reading position; a guide; and a driving unit. The reading unit further includes: a release unit configured to release the contact with the guide by separating the support from the guide when the support is moved toward the predetermined reading position; and a contact portion configured to contact with the support separated from the guide by the release unit when the support is moved toward the predetermined reading position.