To provide a method of increasing the strength of a landslide preventive pile capable of keeping blocks in a steel pipe in a freely movable state independently of the steel pipe even if clamp-pressed and transmitting pressure to the whole of a plurality of blocks to increase deterrent.

In the method of increasing the strength of a restraining pile formed of a steel pipe pile by boring a borehole in a landslide slope to insert the steel pipe pile and then inserting the plurality of blocks in the steel pipe pile, the block 7 inserted in the steel pipe pile 1 has a hole in the center part, and a steel bar 11 with the lower end fixed to a bottom cover 10 fixed to the lower part of the steel pipe pile is inserted in the hole of the block. An upper cover 13 is allowed to pass through the upper end of the steel bar, and the plurality of blocks held between the bottom cover and the upper cover with the steel bar inserted through, are fastened and forcibly pressed by a fastening member 15.

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