A rail apparatus positioned around the surface of a reactor pressure vessel surfaces (1) for carrying equipment such as a flaw detector to permit the equipment to move along the surface of a reactor pressure vessel in the vertical and circumferential directions. The rail apparatus has a plurality of vertical rails (81) and at least one circumferential rail (82) connected to the vertical rails through turn tables (83) at respective points of intersection. Each vertical rail (81) is supported by a supporting member wall fixed at its one end to a gamma-ray shielding wall (2) surrounding the reactor pressure vessel. The vertical and circumferential rails as a unit are retained by the gamma-ray shielding member (84) through oscillation prevention means (86).