To provide a lightweight soil improvement method, simply improving the soil by inserting a pipe support where lightweight filler is enclosed into an improved soil obtained by improving an in-site foundation by soil solidification material and fixing the same to construct a foundation body of lightened structure having strength.

According to this lightweight soil improvement method, the pipe support 1 in which lightweight filler 3 is loaded and enclosed is inserted in an unhardened improved soil 9 obtained by improving in-site foundation by soil solidification material, and the improved soil 9 is consolidated to the pipe support 1 to support a structure. The lightweight filler 3 is made of synthetic resin foam body formed like a solid or beads with a specific gravity equal to or less than that of water.