An image reading apparatus comprises an original placement portion on which an original is to be placed, optical unit for optically scanning the original on the original placement portion while moving relative to the original placement portion and a guide member that guides movement of the optical unit. The optical unit includes a sliding member having a screw portion that slides in contact with the guide member and a screw hole portion to which the sliding member is mounted. The screw portion of the sliding member is plastically deformable and screwed into the screw hole portion while being plastically deformed.