To obtain a rope tensioner device having high durability and allowing monitor of malfunction and maintenance easily.

In this rope tensioner device 21, wherein a fixed evolving force is provided to a ram cylinder 23 for tension, and a span wire 6 wound by a span winch 5 is delivered after winding several times between a plurality of fixed sheaves 25 and a plurality of movable sheaves 27 which are approached to and separated from the fixed sheaves 25 by the ram cylinder 23 for tension, a movable sheave position detector 31 detecting positions of the movable sheaves 27 is provided with a measuring drum 35 winding a measuring wire 33 connected with an output end of the ram cylinder 23 for tension by a cylinder body side, a tension providing mechanism rotatively energizing the measuring drum 35 in a winding direction to provide a fixed tension to the measuring wire 33, and an rotation detector detecting the number of rotations of the measuring drum 35.