Abstract: A sail device characterized in that a sail frame is formed of upper and lower horizontal beam members fixed horizontally to a mast and linealy bent at bending points, holding pillars that are rotatably supported at the above mentioned bending points by these horizontal beam members and that hold a part of a developed sail, and supporting pillars arranged and fixed at both right and left ends of the above mentioned horizontal beam members and assembled rotatably with respect to the horizontal beam members and rotation stoppably by stopper means,at least, between the above mentioned upper and lower horizontal beam members, the lower horizontal beam member is formed to be of a horizontally expanding shape,a sail formed of a flexible material is reinforced by fitting a plurality of self-standing rods in the vertical direction of the sail and the above mentioned self-standing rods can be supported at the lower ends on the above mentioned lower horizontal beam member.