A disk assembly may include: a first disk engaged with a compressor section of a gas turbine; a second disk engaged with a turbine section of the gas turbine; and a third disk disposed between the first and second disks, and transferring torque applied to the second disk to the first disk. The third disk has a plurality of legs formed on an inner circumferential surface thereof, the plurality of legs being in contact with an outer circumferential surface of a tie bolt of the gas turbine.