To stretch a main rope over a roof easily and surely in a short time.

A lower arm 21 located under a roof 11a is secured to the lower part of a main body arm 23 via an inclined position adjustment means 25, and a lower-surface abutting member 29 abutting to the underside of the roof 11a is secured to the end of the lower arm 21. An upper arm 31 located over the roof 11a is secured to the top of the main body arm 23 via a vertical position adjustment means 32, and a pressing means 41 having an upper-surface abutting member 46 in such a way that the member 46 is free to move and pressing the member 46 against the roof 11a is fitted at the end of the upper arm 31. The inclined position of the lower arm 21 and the vertical position of the upper arm 31 are fixed by respective adjustment means 25, 32 to match the inclination and thickness of the roof 11a, the lower-part abutting member 29 is abutted with the lower surface of the roof 11a, the lower arm 21 is abutted with a fascia part 11d, the upper arm 31 is placed over the roof 11a, and the pressure means 41 is tightened.