To provide a cover (54) of a cooling passage that forms a cooling passage (5) for supplying cooling air to a turbine rotor blade at the last stage via inside of a disk (35) of a turbine, and the cover comprises: a cylindrical cover portion (541) that covers a cavity (53) provided in a annular pattern in an outer circumference of the disk (35) in a mode where a first passage (51) opened from inside of the disk (35) to the cavity (53) and a second passage (52) opened from a cooling passage of the turbine rotor blade at the last stage to the cavity (53) are connected to each other; and a flexible portion (542) that is formed integrally with the cover portion (541) and allows flexure in an axial direction of the turbine.