To prevent separation and falling-off of a joint material from a ring-shaped clearance by inserting a spiral reinforcement in a ring shape into an inside part of the ring-shaped clearance formed between a side surface hole of a manhole and a main pipe fitted in this side surface hole, and forming an inside joint by filling the joint material so as to be entangled with this spiral reinforcement.

Metallic wires covered with synthetic resin are wound in a spiral shape, and are juxtaposed in large numbers so that circular parts 6a and small circular parts 6b alternate with each other, and a tightening wire 8 is inserted into the respective small circular parts 6b, and a spiral reinforcement is formed. This spiral reinforcement is bent in a ring shape by putting this tightening wire 8 on the inside, and is inserted into an inside part of a ring-shaped clearance 4 formed between a side surface hole 2 of a manhole 1 and a main pipe 3, and the tightening wire 8 is tightened along an outside surface of the main pipe 3, and both ends are mutually twisted and fastened together (8a), and the total length of the tightening wire 8 is also adhered to an outside surface of the main pipe 3. Next, a joint material 5a such as cement mortar mixed with resin is filled in an inside part of the ring-shaped clearance 4 while entangling it with the spiral reinforcement, and an inside joint 5 to block up the ring-shaped clearance 4 is formed.