release lever 24 that is the release lever 24 is allowed to rotate only through a range which is defined by the hole 24c since the ends of the hole 24c abut against the pin 25 after a predetermined amount of rotation a rod like member 26 is located at a forward end of the swing member 17 and contacts a push button portion 27a of a detector 27 for detecting the runaway of the half speed mirrors 6 and 7 the detector 27 may be a known touch type micro switch which is fixed onto the supporting frame 12 and which provides an on off signal in response to the depression release of the button portion 27a when the push button is relased from the rod like member 26 a signal from the detector 27 is transferred to a known electrical control system not shown so that a power source for driving a supporting frame member 28 of the half speed mirrors 6 and 7 is cut off in response to the signal to stop the scanning operation of the half speed mirrors 6 and 7 assume now that the numerically controlled motor 22 is rotated so that the zoom lens system moves in a direction that enlarges the original document through the feed screw 20 the semiring like nut 19 the swing member 17 and the supporting frame 12 and the zoom lens system stops in a predetermined position from this state the supporting frame member 28 of the half speed mirrors 6 and 7 is moved until it is stopped in a predetermined position corresponding to the copying scale factor and the copying operation is then performed in case the supporting frame member 28 of the half speed mirrors 6 and 7.