To provide a clamping tool for reinforcing a concrete column against earthquakes, as emergency measures to prevent a building which has once escaped collapse in an earthquake from collapsing due to aftershocks, and a clamping method using it.

A tensioning member 2 is a strip with looped joint locking parts 3 and 3' formed at both ends and is wound around a concrete column 1. Support members 4 and 4' projecting in the cross direction of the tensioning strip member 2 are passed through the opposite joint locking parts 3 and 3', and upper and lower projecting parts are connected together by a clamping means 5. The clamping means 5 comprises the support members 4 and 4' each having through holes 4a at both ends, and a clamping fitting 6 passed through the through holes 4a provided in the support members 4 and 4' to connect the support members together. During construction work, the clamping fitting 6 is clamped by use of a tool or the like to apply tension to the tensioning member 2 and a lateral prestress produced by a peripheral compressive force is applied to the concrete column 1.