To contrive stabilization of greening vegetation by attaching a vegetation soil outflow prevention member to the front wall of a futon cage and providing the filling space of vegetation soil on the step part of the crest of the futon cage.

A futon cage is filled with unscreened gravel, gravel soil, floor digging production soil and sand, concrete waste or the like. A vegetation soil outflow prevention member 3 of height which is composed of a plurality of small-diameter logs 5 on the front wall 2 of a one-stage futon cage and in which necessary depth of vegetation soil having a vegetation kind can be secured is mounted. A two-stage futon cage is piled and the step part 1 of the crest of the one-stage futon cage is utilized to provide the filling space 4 of the vegetation soil. The vegetation soil outflow prevention member 3 is attached to the front wall 2 of the two-stage futon cage, and the intrusion gap 6 of a root stem is provided between the small-diameter log 5 of the vegetation soil outflow prevention member 3 and the step part 1. Furthermore, the futon cages of three-stage, four-stage... are piled. Thereby stabilization of greening vegetation can be contrived.