A cover for a cooling passage is disclosed forming a cooling passage for supplying cooling air to a turbine rotor blade at the last stage via inside of a disk of a turbine, and the cover includes a cylindrical cover portion that covers a cavity provided in a annular pattern in an outer circumference of the disk in a mode where a first passage opened from inside of the disk to the cavity and a second passage opened from a cooling passage of the turbine rotor blade at the last stage to the cavity are connected to each other; and a flexible portion that is formed integrally with the cover portion and allows flexure in an axial direction of the turbine.