To facilitate the construction of a slope frame and naturally extinguish the slope frame in due course.

This biodegradable plastic slope frame 1 is formed by combining slope frame members 2 consisting of foamed and molded biodegradable plastics in a frame shape. A natural material such as wood, vegetable fiber, or the like is mixed to the biodegradable plastics followed by foaming and molding. The slope frame member 2 is cylindrically formed, and the natural material is filled in the inner part. This constructing method comprises combining slope frame members 2 consisting of the biodegradable plastics in a frame shape by mutually thermally fusing them. Otherwise, the members are mutually adhered by use of an adhesive consisting of biodegradable plastics, or fixed to a slope by use of a fixing pin consisting of biodegradable plastics.