To provide a reinforcing method for a foundation of a concrete support, which utilizes an existing material, which makes costs low, which makes a construction period short, which enhances constructibility, and which prevents an increase in self-weight.

In this reinforcing method for the foundation of the concrete support elongated in one longitudinal direction on a horizontal plane, the support is fixed to the foundation of the concrete support; a through-hole is provided in the foundation of the concrete support in such a manner as to make a predetermined angle with the horizontal plane in the longitudinal direction, on the circumferential side surface of the support; a continuous fiber sheet and a reinforcing sheet of fiber-reinforced plastics, which is composed of a matrix resin, are stuck on both the longitudinal side surfaces of the foundation of the concrete support; a reinforcing anchor of fiber-reinforced plastics, which is composed of a continuous fiber bundle and a matrix resin, is arranged in the through-hole; and the reinforcing anchor and the reinforcing sheet are joined together.