PURPOSE: To exercise the resistance reducing effect in a turning operation sufficiently while maintaining the easy operating property of a stay, by adapting a frame mast of A-shape.

CONSTITUTION: While a pair of masts 2 with a wing-form section are combined at the tops each other to compose in the reverse V shape, the lower ends of the pair of masts 2 are combined each other by a beam 3 to compose the A- shape frame mast 10, and the lower ends of the frame mast 10 are installed tiltable in the longitudinal direction on the boat body. And an extrusion 4 to which the front edge of a sail 5 is installed is provided between the center in the boat width direction of the beam 3 and the top of the mast, while the front end of a boom 6 is installed at the center in the width direction of the beam 3 so that the boom 6 can be fluctuated within the horizontal plane, and also the masts 2 are fluctuated linking to the fluctuation of the boom 6.