PURPOSE: To prevent in advance an accident caused by a strength drop by covering a metallic line of a fluid transport pipe with an electric insulator, detecting a conduction which is generated between the metallic lines due to a fact that the covering is eliminated by abrasion of the electric insulator, and diagnosing the deterioration of the fluid transport pipe.

CONSTITUTION: A fluid transport pipe 1 consists of a plastic inner pipe 2, a metallic reinforcing layer 4 formed by winding spirally plural metallic lines 3 thereon, and an external sheath 5 made of plastic, and the outside peripheral surface of the metallic line 3 is covered with an electric insulator 6. In this state, a lead wire 8 is connected to end parts 3a, 3b of each metallic line of the reinforcing layer 4 from a terminal part of the transport pipe 1 and a voltage is applied, and a part thereof or the whole is eliminated due to abrasion of the electric insulator 6 and a current generated between the metallic lines 3 is detected.