PURPOSE: To allow the easy positioning of an operating shaft at a prescribed angle by providing a locking lever which fixes a locking plate formed with engaging parts for every assigned turning angle of the operating shaft to the operating shaft and engages the shaft to the engaging part and an unlocking lever which releases the engagement of this locking lever.

CONSTITUTION: A turning knob 35 is rotated while an unlocking pin 34 is held pressed when, for example, the operating shaft 28 is to be turned in order to change the photosensitive material guide width of a printer processor. The locking state of the locking lever 51 with the locking plate 55 is released by the pushing of the unlocking pin 34 and the turning of the operating shaft 28 is enabled. The operating shaft 28 is turned via transmitting means 46 to 48 when the turning knob 35 is thereafter turned. The locking plate 55 is locked in the next locking position when the shaft turns by a prescribed angle and, therefore, the operating shaft 28 is prevented from turning more than this point. Thus, the operating shaft is easily positioned at the prescribed turning angle and the setting to the desired guide width is possible by repeating the similar operations thereafter.