A speed reducing mechanism includes a speed reducer and a bearing engaged with the speed reducer. The speed reducer includes a driving member, a first transmission member and a second transmission member. The driving member is connected to the first transmission member. The first transmission member forms a plurality of first engaging teeth, and the second transmission member forms a plurality of second engaging teeth. The total number or count of the first engaging teeth is different from that of the second engaging teeth. The bearing includes a bearing cone, a bearing cup, and roller bearings mounted between the bearing cone and the bearing cup. The first transmission member is fixed to the bearing cup, and the second transmission member is fixed to the bearing cone.