Each of embodiments provides a power transmission device of a steering apparatus including: a first shaft that has an one-side end at which a coupling end of which a diameter is reduced and formed is provided; a second shaft that has an end facing the first shaft at which a coupling groove into which the one-side end of the first shaft is inserted is provided; and an elastic support member having an inner circumferential face into which the coupling end is inserted and an outer circumferential face that is supported on and coupled with an inner circumferential face of the coupling groove.