Method for inspection and maintenance of an inside of a nuclear power reactor

A method for inspection and maintenance of an inside of a nuclear power reactor is provided, which can perform positioning of a remote operated vehicle relative to an inspection target surface in a nuclear power reactor in a short period of time with high accuracy, and enhance the positioning repeatability for the remote operated vehicle, thereby enabling performance of the inspection and maintenance for the inspection target surface securely and satisfactorily. For the inspection or maintenance for the inspection target surface 1 a in a nuclear power reactor by using the remote operated vehicle 30, a detection mark 3 is formed in advance by providing a notching, marking, punching or engraving process to the inspection target surface 1 a before performing inspection or maintenance of the inside of the nuclear power reactor by using the remote operated vehicle 30. Then, the remote operated vehicle 30 is driven to move in the nuclear power reactor filled with water. During the movement, the detection mark 3 formed in the inspection target surface 1 a is detected by using the remote operated vehicle 30 so as to determine the position of the remote operated vehicle 30.