PURPOSE: To smoothly wind a sail by providing a boom supported by the mast of a sailing boat with a winding member freely rotationally supported at its first end, and forming the member so that its diameter increases from the first end to a second end.

CONSTITUTION: A main sail rigging 10 includes a mast 12, a boom 14, and a main sail 16, and the main sail 16 is connected to the boom 14 at its bottom and to the track 20 of the mast 12 at its vertical edge via a luff bead 18. In this case, the boom 14 is rotatably attached to the mast 12 and made to function as a winding member, with its rotation enabling the main sail 16 to be wound around it. The boom 14 is formed into a shape such that its diameter increases from an end 22 near the mast 12 to the opposite end 24, that is, a conical shape.