The invention provides a dovetail structure of a fan which attaches a fan 20 having an inlet hub diameter smaller than an outlet hub diameter to a portion around a discoid disc rotationally driven by a turbine. The disc 10 has a plurality of dovetail grooves 12 extending at a fixed angle θ1 with respect to an axis 1 of a rotation axis from a leading edge 10a to a trailing edge 10b thereof, and spaced at a fixed angle in a peripheral direction. The fan 20 has a dovetail portion 22 extending at the same angle as an angle of the dovetail groove and capable of being fitted to the dovetail groove, in an inner end thereof.