To easily install a multiple cable protection tube buried underground, even is a constitution site is narrow, for space saving, and also to make construction works easy such as stacking of the multiple cable protection tubes.

A filler member, capable of setting interval between tubes, whose upper and lower sections are flat while left and right sections correspond to the profile of the protection tube, is installed in the gap between the protection tubes constituting the multiple cable protection tube. So, the stacking of the multiple cable protection tube is made easy and irregular subsidence of the ground surface will not occur, even at a narrow site.