To measure a strength of a concrete in the degree of a slight damage by injecting a water jet of a constant energy, drilling a structure concrete, and measuring a compression strength of the concrete.

The apparatus 1 for measuring a strength of a structure concrete generates a water jet W of a constant energy (a constant amount and a constant pressure) by a pump 2, injects a water jet W from a nozzle 3, and drills a structure concrete 8. A depth measuring instrument 5 provided in a water supply passage in the rear side of the nozzle 3 measures a depth of the drilled hole of the concrete 8 real time. A calculator 6 inputs output data of the instrument 5 through an electric cable 15, and divides an increment of a displacement of the depth of the hole by its predetermined time to calculate a drilling speed. The strength of the concrete is measured in real time from a relational formula between the drilling speed and the strength of the concrete. Thus, since the degree of the damage to the structure can be made slight, the influence on a yield strength of the structure is small.