A power transmission device for an image forming apparatus, comprising: a first rotary body including a first gear configured to be rotated by a driving force from a drive source, the first rotary body being disposed on a drive source side on a power transmission path through which the driving force is transmitted from the drive source to a driven member; a second rotary body including a second gear disposed on a driven side on the power transmission path; and a third rotary body including a third gear disposed on the power transmission path configured to transmit the driving force to the second rotary body by meshing with the first gear and the second gear, the third rotary body being movably held within a power transmittable range; and a guide member (107f, 106f, 108a) disposed at one of the first gear, the second gear, and the third gear configured to contact a first end surface of a gear tooth of another of the first gear, the second gear, and the third gear serving as a mating gear, to guide the first end surface of the gear tooth of the mating gear between gear teeth of the one of the first gear, the second gear, and the third gear, the guide member (107f, 106f, 108a) extending toward the mating gear in an axial direction of the one of the first gear, the second gear, and the third and a tip of the guide member (107f, 106f, 108a) being spaced apart a predetermined distance from an end, adjacent said mating gear, of the one of the first gear, the second gear, and the third gear in the axial direction; characterised in that the guide member (107f, 106f, 108a) is one of the gear teeth of the one of the first gear, the second gear, and the third gear, and extends beyond other gear teeth in the axial direction toward the first end surface for a predetermined distance. a first rotary body including a first gear configured to be rotated by a driving force from a drive source, the first rotary body being disposed on a drive source side on a power transmission path through which the driving force is transmitted from the drive source to a driven member; a second rotary body including a second gear disposed on a driven side on the power transmission path; and a third rotary body including a third gear disposed on the power transmission path configured to transmit the driving force to the second rotary body by meshing with the first gear and the second gear, the third rotary body being movably held within a power transmittable range; and a guide member (107f, 106f, 108a) disposed at one of the first gear, the second gear, and the third gear configured to contact a first end surface of a gear tooth of another of the first gear, the second gear, and the third gear serving as a mating gear, to guide the first end surface of the gear tooth of the mating gear between gear teeth of the one of the first gear, the second gear, and the third gear, the guide member (107f, 106f, 108a) extending toward the mating gear in an axial direction of the one of the first gear, the second gear, and the third and a tip of the guide member (107f, 106f, 108a) being spaced apart a predetermined distance from an end, adjacent said mating gear, of the one of the first gear, the second gear, and the third gear in the axial direction; characterised in that the guide member (107f, 106f, 108a) is one of the gear teeth of the one of the first gear, the second gear, and the third gear, and extends beyond other gear teeth in the axial direction toward the first end surface for a predetermined distance.