PURPOSE: To widen wind directions to be utilized and enhance the wind force characteristic of a sail by revolving a stay which supports the sail mast, and allowing the sail to revolve interlocked with the first named revolution.

CONSTITUTION: A mast 4 is put upright on the deck 101 of a hull 100 rotatably round a shaft, and bottoms of stays 1a, 1b, 1c supporting it are coupled with a circular guide 3. This circular guide 3 is supported and guided by a stationary guide 2 stretching up the hull 100 so as to be free to revolve. Accordingly the sail is capable of revolving in a single piece with the mast 4 and stays 1a, 1b, 1c. In case the mast 4 is fixed, such members to cause revolutions as the stays 1a, 1b, 1c, sail beam 5, and sail are coupled with the mast 4 through a bearing so as to allow only the sail and stays to revolve.