Abstract: A speed reducer is provided with a shock absorbing rubber damper disposed in a power transmission path from a first wheel to which a driving force of a motor is input to a second wheel from which the power is output. First projecting portions 3e and auxiliary projecting portions 3f are provided on a first wheel. Second projecting portions 5b are provided on a second wheel 5. The projecting portions are disposed together in intervals T defined between segmented rubber dampers 6. Receiver plates 7, 8 are attached to the end surfaces 6a, 6b of the rubber dampers 6 and serve as load bearing surfaces confronting the projections 3e, 3f and 5b so as to approximately distribute the loads over the entire end surfaces. Two receiver plates 7, 8 disposed across the end surfaces 6a, 6b can be arranged as an integral receiver plate unit U. With this arrangement, a shock absorbing capability is enhanced as well as the number of parts can be reduced.