To provide an unnecessary buried pipe filling method that can be performed with a small number of times for excavation for working pits, and also can reduce construction time and labors, costs, and period of time.

In the unnecessary buried pipe filling method, two-place working pits 15, 15 are formed at separate position road surfaces, and both ends of an unnecessary buried tube 2 exposed at each working bits 15, 15 are sealed by an injection side flange 3 and stopper-attached flange 4. Herein, when a water-soluble urethane compound in a chemical tank 9 is filled from a chemical injection pipe 7 and a great deal of water W in a water tank 12 is filled, the water-soluble urethane compound is dissolved in a great amount of water W to become a solution to spread to every corner in the unnecessary buried pipe 2. After that, the urethane compound in the solution and water W are reacted with each other, so that highly hydrous foam polyurethane 16 having closed cells 17 is formed in the pipe.