PURPOSE: To enable both manual and power operation through a simple structure, by engaging a plurality of planetary gears with a sun gear being driven through a drive source and with an internally rollable gear capable of engaging with a warm being rotated through a manual handle.

CONSTITUTION: When a sun gear 6 is rotated by a drive source 7, an internally rollable gear 8 does not rotate because of a high reduction ratio with respect to a warm 10 which causes a high resistance, thereby a plurality of planetary gears 4 spin while simultaneously revolve around the sun gear 6. Since the sun gear 6 is arranged concentrically with the main shaft 3 of valve for opening/ closing a valve 2, the planetary gears 4 rotate around the center of said shaft 3. When the internally rollable gear 8 is rotated by a manual handle 11 through the warm 10, a plurality of said planetary gears spin while simultaneously revolve around the sun gear 6.