A preventive maintenance/repair device arranged for maintaining and repairing a cylindrical structure among reactor internal structures installed in a reactor pressure vessel, and comprising: a device body; a holding mechanism (13a, 13b) connected to the device body, the holding mechanism being configured to hold the device body on an outer circumferential surface of the cylindrical structure and including: a pair of arms (12a, 12b) each having a shape along the outer circumferential surface of the cylindrical structure; guide rollers (14a, 14b) respectively disposed on distal ends of the pair of arms; arm cylinders (17a, 17b) configured to respectively drive the pair of arms; and links (18a, b) connected between the arms and the arm cylinders, the links being configured to transmit drives of the arm cylinders to the arms; a traveling and driving part disposed on the device body, the traveling and driving part including a traveling wheel arranged to rotate in contact with the outer circumferential surface of the cylindrical structure, so as to move the traveling and driving part along the outer circumferential surface of the cylindrical structure; and a maintenance/repair mechanism disposed on the holding mechanism and arranged for maintaining and repairing the cylindrical structure characterized in that an access device is removably mounted to the device body and in that an operation pole is connected to the access device, the operation pole being configured for bringing the device body to the cylindrical structure so as to attach the device body to the outer circumferential surface thereof and the access device may be removed from the device body, once the device body is held on the cylindrical structure by the holding mechanism. a device body; a holding mechanism (13a, 13b) connected to the device body, the holding mechanism being configured to hold the device body on an outer circumferential surface of the cylindrical structure and including: a pair of arms (12a, 12b) each having a shape along the outer circumferential surface of the cylindrical structure; guide rollers (14a, 14b) respectively disposed on distal ends of the pair of arms; arm cylinders (17a, 17b) configured to respectively drive the pair of arms; and links (18a, b) connected between the arms and the arm cylinders, the links being configured to transmit drives of the arm cylinders to the arms; a pair of arms (12a, 12b) each having a shape along the outer circumferential surface of the cylindrical structure; guide rollers (14a, 14b) respectively disposed on distal ends of the pair of arms; arm cylinders (17a, 17b) configured to respectively drive the pair of arms; and links (18a, b) connected between the arms and the arm cylinders, the links being configured to transmit drives of the arm cylinders to the arms; a traveling and driving part disposed on the device body, the traveling and driving part including a traveling wheel arranged to rotate in contact with the outer circumferential surface of the cylindrical structure, so as to move the traveling and driving part along the outer circumferential surface of the cylindrical structure; and a maintenance/repair mechanism disposed on the holding mechanism and arranged for maintaining and repairing the cylindrical structure characterized in that an access device is removably mounted to the device body and in that an operation pole is connected to the access device, the operation pole being configured for bringing the device body to the cylindrical structure so as to attach the device body to the outer circumferential surface thereof and the access device may be removed from the device body, once the device body is held on the cylindrical structure by the holding mechanism.