To improve the reliability of the lubricating performance by providing a circular oil sump part in the outer periphery part of an annular cover and an oil receiving part which guides to the oil sump part thereof, and also providing an oil passage which connects a lubricating necessary part of a planetary gear and a base end of the oil sump part in a shaft supporting part of the planetary gear of a carrier.

A circular oil sump parts 27c which open toward an inner circumference and extend from a base end of covering parts 27b to a rotating direction of a carrier 22 is provided in the outer periphery part of an annular cover 27. Oil receiving parts 27d, 27e are also provided which scrape up the lubricating oil around a cover 27 by a rotation of the cover 27 to guide to an oil sump part 27c. Oil passage 24a which connect a lubricating necessary part of a planetary gear 25 and a base end of the oil sump part 27c are further provided in axis supporting parts 24 of the planetary gear of carriers 22. Thereby, the lubricating necessary parts of a planetary gear 25 are lubricated surely to improve the reliability of the lubricating performance.