To improve the aseismatic performance of existing concrete piles of an existing building with a good execution property at a low cost by spirally winding a material having tension resistance performance on the reinforcement object portions of the existing concrete piles of the existing building, then spraying mortar or concrete.

When aseismatic reinforcement is to be applied to hollow existing concrete piles 3, 3 already driven in the ground as the foundation piles of the foundation 2 of an existing structure 1, the ground below the foundation 2 is excavated until the pile head sections 3A, 3A of the existing concrete piles 3, 3 are completely exposed. When an excavation bottom 5 becomes a level lower than the reinforcement object portions of the existing concrete piles 3, 3, multiple spacers 6 are installed along the axial direction on the surfaces of the pile head sections 3A, 3A after cleaning. A PC steel stranded wire 7 is spirally wound on the pile head sections 3A, 3A from above the spacers 6, mortar or concrete 8 is sprayed, and the pile head sections 3A, 3A are back- filled.