According to one embodiment, a method is used for diagnosing a deterioration of a utility pole having at least one bolt and a plurality of holes provided for attaching the bolt. In the method, an impact is applied to the bolt. Elastic waves generated due to the impact are detected by a sensor shaped like a bolt. The sensor is attached to at least one of the holes. A propagation situation of the elastic waves in the utility pole is derived, based on the elastic waves detected, and each position of the bolt and the sensor.