An eccentric oscillating gear device comprises a crankshaft having an eccentric portion, an externally toothed gear having external teeth and a through-hole in which the eccentric portion is inserted, an outer cylinder, and a carrier. The carrier rotatably supports the crankshaft. The outer cylinder has internal teeth meshed with the external teeth of the externally toothed gear. The eccentric oscillating gear device is provided with rotational phase adjusting section for setting an orientation of the crankshaft about an axis thereof, on the basis of orientations of the outer cylinder and the carrier about an axis thereof.