To provide an eccentric type reduction gear wherein an eccentric portion and an intermediate portion of a crank shaft are held by a bearing, for suppressing an increase in the axial length of the crank shaft by increasing the number of roller members which can be arranged in the bearing.

A first specified member 56 having a first cavity portion 56a into which a first eccentric portion 23a is inserted is arranged at one end of the crank shaft 23. A second specified member 57 having a second cavity portion 57a into which the first eccentric portion 23a is inserted is arranged between the first eccentric portion 23a and the intermediate portion 23e. The first specified member 56 and the second specified member 57 restrict the position of a first external tooth bearing 53 holding a first external gear 28a, in the axial direction of the crank shaft 23.