Maintenance system for a reactor incore piping section

An incore piping section maintenance system of a reactor comprises a maintenance system main body which is fixed to a maintenance target protion in a reactor pressure vessel or in the vicinity thereof to which a preventive-maintenance operation is executed, a support mechanism provided for the maintenance system main body so as to be movable in a reciprocal manner towards the maintenance target protion, a laser generator for generating a laser beam, a laser de-sensitization treatment apparatus which is rotatably supported around an axis of the support mechanism and which includes a laser irradiation section for irradiating the laser beam to the maintenance target portion and an optical transmission element which guides the laser beam outputted from the laser generator to the laser de-sensitization treatment mechanism.