In a turbine disk and a gas turbine, the turbine disk is firmly connected to a rotor (24) to be rotatably supported; a plurality of rotor blades (22a) is arranged on an outer circumference thereof in a circumferential direction; first cooling holes (42) penetrating the turbine disk from inside toward outside thereof and being communicatively connected to a cooling passage (41) arranged inside of the rotor blades (22a) are arranged in the circumferential direction; second cooling holes (43) arranged between each of the first cooling holes (42) and penetrating the turbine disk from the inside toward the outside thereof are provided; and the first cooling holes (42) and the second cooling holes (43) are communicatively connected by way of a radial direction communicating channel (47), to alleviate concentration of stress and to improve durability.