PURPOSE: To greatly raise the efficiency of constructing operation by a method in which an invert block divided into two symmetrical parts having a fan-like pattern is carried into the upper opening of a manhole constructed and assembled to position it with the inflow and outflow pipe of a dog leg shaped block.

CONSTITUTION: Invert blocks 31 and 32 divided into two symmetrical parts having the same curvature radius as the circular arc part of a dog leg shaped block and also having a fan-like pattern are carried into the upper opening of a manhole 5 constructed and assembled on the bottom slab 54 of the lower end. The flowpath grooves of the blocks 31 and 32 are positioned on the inflow and outflow pipes 61 and 62 of the dog leg shaped block 6. A filler is packed into the aperture between the facing ends of the blocks 31 and 32 to form partly a flow path and invert face. Cement mortar 71 is packed into the aperture between the circular arc part and the block 6. The constructing operation efficiency can thus be greatly raised by easily matching a variation of flow paths.