Patent ID: 7894106

Claim:
An image reading device, comprising: a running unit on which a scanning optical system that optically scans a document is mounted, the running unit moving in a case; a driving-force transferring unit that is extended in a predetermined direction, of which a predetermined portion is attached to the running unit; a driving unit around which the driving-force transferring unit is wound, the driving unit changing a direction of movement of the driving-force transferring unit by rotating in a forward direction or in a backward direction based on a driving force from a driving source; and at least one pulley unit that is rotatably attached to the case and supports the driving-force transferring unit, wherein the pulley unit includes: an outer ring member that is rotated by the driving-force transferring unit; an inner ring member that rotatably supports the outer ring member; and an engaging unit that is provided on the inner ring member, to engage with the case, wherein the engaging unit is symmetric on both sides with respect to a plane including a center shaft of the inner ring member, one end portion of the driving-force transferring unit is attached to the inner ring member via a spring member, the inner ring member includes a spring engaging unit to be engaged with the one end portion of the driving-force transferring unit, and the spring engaging unit is disposed on a symmetrical position with respect to a surface including a center axis of the inner ring member.