PROBLEM TO BE SOLVED: To provide a diagonal member inspection device capable of inspecting presence/absence of damage and fracture of PC steel wires constituting diagonal members of a cable-stayed bridge in an unmanned manner by teleoperated control, and diagonal member inspection method.SOLUTION: The diagonal member inspection device includes transfer means, imaging means, inspection means, control means, and batteries. The transfer means includes a pair of driving wheels for clamping a cable and being closely fitted to a surface of the cable. The imaging means acquires image data of the surface of the cable. The inspection means is movably disposed on an annular path disposed along the outer periphery of the cable and measures impedance of a coil causing the cable to generate an eddy current. The control means operates the transfer means, the imaging means, and the inspection means on the basis of a control signal transmitted from a ground side, and transmits data acquired by the imaging means and the inspe
