An image reader includes a casing, a contact glass plate, a contact image sensor, and a sliding mechanism; wherein the contact image sensor has a housing, a light source attached to the housing so as to face the contact glass plate, a plurality of light receiving elements attached to the housing so as to face the contact glass plate and aligned in parallel in a longitudinal direction of the housing, and a bearing formed integral to the housing at a position below a lower surface of the housing; and the sliding mechanism includes a guide shaft provided on the casing and extending in a short direction of the housing and inserted through the bearing, and an urging member elastically which urges the guide shaft toward the contact glass plate so that the housing is pressed against the contact glass plate.