To provide a degradation inspecting method for a concrete structure for easily, efficiently and highly accurately detecting degradation by alkali aggregate reaction or the like of an erected concrete structure.

A weight 8 is dropped from a predetermined height onto upper concrete 2 of an erected pier, and the amounts of vertical displacement are measured by deflection sensors 6a, 6b respectively at a drop point Pcx formed by the drop of the weight 8 and at a peripheral point Pnx distant by a predetermined space from the drop point Pcx. The degraded degree of the upper concrete 2 is determined based on the comparison between the measured amounts of vertical displacement.