A purpose of the present invention is to provide a diversity receiver and a diversity receiving method, which are capable of performing a diversity reception without depending upon a moving speed, and also capable of achieving compatibility between reception performance and current consumption. The endless flexible belt is looped into a generally cylindrical configuration extending in an axial direction thereof for rotation in a rotational, circumferential direction thereof. The photoresist film is exposed and then developed to form a fine resist pattern 4 with 0. The LiNbO3 phase modulator imprints an RF signal onto one path of the MZM cavity, while the fiber wrapped PZT is used to control the path length difference between the two optical paths. The invention is a diagnostic method for an oil-filled electrical device including in an insulating oil a metal part wrapped with insulating paper, and determines that a time when a surface resistivity of a maximum precipitation site where metal sulfide is most precipitated on the insulating paper reaches a preset surface resistivity management value is a time of occurrence of an abnormality. The method also includes storing the knowledge network in the master knowledge repository, and providing access to the stored knowledge in the knowledge network.