To simply, certainly and economically carry out concrete formwork construction to reinforce an existing pillar type structure.

Concrete is continuously deposited by arranging a pair of half part formwork bodies A, A connecting two pieces of surface formworks 1a, 1b provided with a plural number of interval adjusting rods 31, 31 free to adjust them to get in and out with intervals in the lateral direction and in the vertical direction in the circumference of an existing pillar type structure B, setting head ends of the interval adjusting rods 31, 31 by keeping a required clearance (a) by making them contact with a side surface of the existing pillar type structure B and removing the interval adjusting rods 31, 31 after depositing reinforced concretes C-C3 to a lower position near the interval adjusting rods 31, 31.