PURPOSE: To enable a bending moment applied to a cable connecting box, to be reduced, by arranging seat beds in a space between the cable connecting box and the bottom surface of a hand hole, when the cable connecting box is set in the hand hole.

CONSTITUTION: When a cable connecting box 4 is set in a cable connecting section laying directly-embedded trough (a hand hole) 1, then seat beds 10 are arranged in a space between the cable connecting box 4 and the bottom section of the hand hole 1, and both the end sections of the cable connecting box 4 are supported. The hand hole 1 is filled up with sand. As a result, a bending moment applied to both the end sections of the cable connecting box 4 is reduced, and so the cable connecting box 4 can be installed with safety.