Abstract: In a method and a system for inspection of the inside of a nuclear reactor vessel in which an inspection device for inspecting a defect in a nuclear reactor vessel is so moved by a drive/control device as to permit inspection of a part to be inspected in the reactor vessel, and the presence or absence of defect in the reactor vessel is judged based upon information from the inspection device in the course of the above-mentioned movement of the inspection device; the movement of the inspection device is pursued and monitored by monitor means, and the movement of the inspection device is suppressed when an abnormality in the movement of the inspection device is judged based upon information from the monitor means, to avoid the abnormal movement.