Patent attributes
A reduction gear includes a reduction mechanism and a component which constitutes the reduction gear and in which a cavity portion is provided. The reduction mechanism is not provided in the cavity portion. The component includes a reinforcement structure which is provided to partially fill an inside of the cavity portion and forms a void, which is filled with air or fluid, in the cavity portion. The cavity portion includes only one opening with respect to a space in which the reduction mechanism is accommodated or with respect to an external space, or the cavity portion is provided so as to form a closed space inside the component.