DRIVING FORCE TRANSMITTING DEVICE

PROBLEM TO BE SOLVED: To prevent backlash and eccentricity in a rotating direction between a gear to be driven and a rotary shaft with simple constitution and to easily change a gear by forming a key groove on the rotary shaft and forming a key engaged in the key groove of synthetic resin having elasticity integrally formed with the gear to be driven. SOLUTION: A screw hole is formed along the axis of the rotary shaft 27, and the key groove is formed in parallel with a shaft on the peripheral surface of the shaft 27. The key extended in the axial direction and fit in the key groove of the shaft 27 is integrally formed with the gear to be driven 30 on the inner peripheral surface of the hollow part of the gear 30. After the gear 30 is perfectly fit to the shaft 27, a bolt 31 is driven into the threaded hole of the shaft 27, so that the gear 30 is perfectly fixed on the shaft 27 of a driving roll 2. Thus, the backlash in the rotating direction is prevented. Since the gear 30 and the key are integrally formed of resin, production cost is reduced.