To provide a tension device in which a nut is easily screwed with a shaft of a fastening tool, and the shaft of the fastening tool is not susceptible to cause obstruction.

The shaft 38 of the fastening tool 31 is constituted of a main body shaft 44 on a wire body side, and a separate shaft 4 which has a male screw separably screwed and connected with a female screw which is formed at the end part of the main body shaft 44 on a side separated form the wire body. The separate shaft 47 has a thin part 48 formed to one end side screwed and connected with the main body shaft 44 so that a nut 36 can rotate around the thin part. The length of the thin part 48 is set not so that one nut 36 can be screwed with the male screw 37 of the main body shaft 44 and the male screw 37 of the separate shaft, and in addition to this, one of contiguous two nuts 36 can be screwed with the male screw 37 of the main body shaft 44 and the other nut 36 can be screwed with the male screw 37 of the separate shaft 47.