To solve the following problems that, in a conventional method of forming a composite pile of a soil cement pile and a steel pipe pile, after the formation of the soil cement pile, the steel pipe pile is embedded anew, and therefore not only both a soil cement pile forming device and a steel pipe pile embedding device are necessary, but also setup must be changed resulting in complicated construction procedures to thereby cause inconvenience in terms of construction efficiency and construction cost, in a method of embedding a steel pipe pile having a spiral blade mounted thereon, earth around the steel pipe is disturbed by the spiral blade due to the rotational press-fitting of the steel pipe pile, and therefore pile peripheral friction cannot be expected only by a support force of an area of the spiral blade, in the same method, a water content in the earth around the steel pipe pile causes the corrosion etc. of the steel pipe pile over a long period of time.

There is provided a new method of forming a composite pile of a soil cement pile and a steel pipe pile. According to the method an accompanying rotation prevention plate is arranged on an excavation blade and an agitation blade, and between the former and the latter, and an ejection port is formed at the tip of the steel pipe pile for ejecting cement milk. Then while the steel pipe pile itself is rotated, the cement milk and soil are mixed and agitated to form the soil cement pile, and at the same time, the steel pipe pile is driven into the ground at a predetermined depth.