PURPOSE: To improve power transmission efficiency and durability by providing a projecting portion having a section formed with a part of circle on one face of a block while providing a projecting-out portion on which a recessed portion consisting of a part of a circle and a straight line portion is formed on the other face and fitting the projecting portion to the recessed portion of an adjacent block.

CONSTITUTION: A block body 5, a power transmitting portion 6, and a middle portion 4 placed in the middle of these are provided, and both side portions of the power transmitting portion 6 are formed into power transmitting faces 7 which are formed at the same angle as the inclination of the V-groove of a pulley while forming carrier fitting engaging grooves 8 on both sides of the middle portion 4. Also, an inclined face and a projecting portion 13 of a part of circle whose center is on a pitch line are provided on the front portion 12 of the power transmitting portion 6 while providing a projecting-out portion 15 having a circular long-hole shaped recessed portion 14 consisting of a part of the combination of two circles having the same radius as that of the projecting portion 13 and straight line portions on the back face thereof. Hence, each projecting portion and recessed portion of adjacent blocks is fitted to the other to form a hinge portion, enabling expansion/contraction and bending while improving the efficiency of power transmission and durability.