PURPOSE: To enable the safety of a bicycle travel and a driving posture matching travel conditions by fixing, inside of a lock ring, a curved surface lock claw having the same diametrical circumference with a protractor plate to prevent left/right handles from returning to this side, and providing a means to lock doubly left/right handle base parts.

CONSTITUTION: As for an angle A condition, when a lock claw 13a is inserted inside of a rotary ring in a position where the side surface 2e of a protractor plate 2a of a left handle 2 and the side surface 2m of a protractor plate 2j of a right handle 2 butt each other, the side surface 13c of the lock claw 13a butts the side surface 2d of the protractor plate 2a of the left handle 2, and the side surface 13d of the lock claw 13a butts the side surface 2n of the protractor plate 2j of the right handle 2, and a circle of 360 degrees is formed, and the left/right handles 2 can be locked so as not to return to this side. As for an angle B condition, when the left/right handles 2 are turned to this side until the side surface 2d of the protractor plate 2a of the left handle 2 butts the side surface 13g of a lock claw 13e and the side surface 2n of the protractor plate 2j of the right handle 2 butts the side surface 13h of a lock claw 13e, the left/right handles 2 can be locked.