PURPOSE: To always accurately perform actions in a stable state and to improve image quality by providing a wire tensile force varying mechanism consisting of a tension wire pulley, a solenoid and a driving force transmission member, which comes in contact with a part of the distributing system of a wire.

CONSTITUTION: The wire tensile force varying mechanism 9 is provided, which changes the rate of the tension applied to the wire 4 at the time of reading and scanning and at the time of returning. The mechanism 9 is formed of the tension wire pulley 10 which comes in contact with a part of the distributing system of the wire 4 from the outside, the solenoid 11 and a plunger 12 functioning as the driving force transmission member for transmitting the driving force of the solenoid 11 to the pulley 10. Therefore, in the case of reading and scanning, the tension of the wire 4 is made low and the sliding force of a scanner 2 becomes weak. Thus, the actions are always accurately performed in the stable state and the image quality is much more improved.