PROBLEM TO BE SOLVED: To provide a construction method suitable for construction of a pile reinforcement structure in which ground around a pile is removed to expose the pile, and reinforcement material such as aggregate is input into the removed space for compaction to form a reinforcement layer.SOLUTION: A construction method of a pile reinforcement structure in which a pile 2 is driven into ground 1, and a reinforcement layer is formed around the pile 2, includes preparing an auger 4 having a cylindrical part 5 whose diameter is larger than that of the driven pile 2, and a blade 6 formed on the circumference of the cylindrical part 5, and rotating the cylindrical part 5 while externally inserting it to the pile 2 and inputting solidification material 10 into an area around the pile 2 from the cylindrical part 5.
