PURPOSE: To tightly retain and fix a mast in position by forming downward an engaging tooth part in the longitudinal groove of a sailing boat and mounting a foot-stepping locking means which is engaged with the engaging tooth part, on a supporting device with which the mast is coupled via a journal joint.

CONSTITUTION: A step guide 16 installed in a groove which is formed in the longitudinal direction of a sailing boat has a downwardly formed engaging tooth part 34 running along both sides thereof. A locking means 20 consisting of a ratchet member 120 which is urged upward by a spring 122 and has a foot- stepping operating part 124 on the upper part thereof is installed on a supporting device 68 with which the lower part of a mast 30 for a sail attached thereto is coupled via a journal joint 110. The engaging relation between the engaging tooth part 34 and the ratchet member 120 is released by pressing the foot- stepping operating part 124 downward and after it is moved to a specified position, the stepping by foot is released. The mast may be tightly retained and fixed in the specified position.