A gear structure of the present invention comprises a first gear and a second gear. A teeth portion constituting a gear portion of the second gear are provided, in a partial area in its tooth width direction, with regulating portions formed into a shape which is cut so as to have a diameter smaller than an external diameter of a tooth top. Furthermore, the first gear is provided with fitting portions into which the regulating portions of the second gear are fitted. The regulating portions of the second gear are fitted into the fitting portions of the first gear so that they may be integrally stacked and arranged.