A detecting device for performing fatigue tests on a pivoting piece includes a clamping module and an actuating module. The clamping module clamps the pivoting piece. The actuating module includes an elastic actuating shaft abutting the clamping module and a resilient member mounted in the elastic actuating shaft. The resilient member is adapted to push forward against spring pressure and retract by the release of spring tension so as to achieve cyclic movements in the pivoting piece.