To easily measure the depth of a branch pipe from a sewage main pipe without executing excavating construction work.

An insertion jig 12, i.e., a transmitter 11, is inserted into a branch pipe 25 from a sewage meeting place 24. A road surface side jig 5 is installed in a position a prescribed length a (an installation length a) on the center side of a road from the side of the road on a road surface in a corresponding place in the vertical direction above the branch pipe 25. The posture of the road surface side jig 5 is adjusted with a level. In this state, an insertion rod 10 is pushed and pulled, a position in which the number of turned-on lamps is most is searched by a verticality judgment means, and the rod 10 is stopped. In a state that the insertion of the insertion rod 10 is stopped, an insertion length (c) in a position just under the side of the road is read out. Since a depth (b) down to the bottom in the sewage meeting place 24 is known in advance, a depth (x) up to the transmitter 11 from the road surface is found on the basis of the depth (b), the installation length (a) and the insertion length (c), the wall thickness of the branch pipe 25 is added to the depth, and the depth of the branch pipe 25 is measured.