A driving mechanism including a stepping motor having a rotor which rotates through a certain angular interval each time the stepping motor is energized. A driving member having a plurality of radial slots is mounted for rotation about an axis and is rotated by the rotor. A driven member is mounted for rotation and includes a pin extending therefrom for engaging one of the slots as the driving member rotates and for disengaging from the one of the slots after the driving member has rotated past the certain angular interval, whereby the driven member is rotated through the certain angular interval upon energization of the stepping motor. The driving member includes arcuate peripheral portions over a limited angular extent and concentric with the axis of rotation of the driving member. The driven member includes concave arcuate portions of limited angular extend spaced about the periphery thereof. The driven member is rotatable to a position so that one of the arcuate portions is concentric with the axis of rotation of the driving member and extends along and opposite an arcuate peripheral portion of the driving member for preventing rotation of the driven member when an arcuate peripheral portion of the driving member and one of the corresponding concave arcuate peripheral portions of the driven member are opposed when the stepping motor is not energized.