A gear unit (1, 101) for transmitting torque, at a predetermined reduction gear ratio, between a pair of partner members which are relatively and rotatably coupled to each other, the gear unit (1, 101) comprising: an outer cylinder (2, 102) configured to be fixed to one of the partner members; a plurality of internal gear pins (3, 103) which are mounted on an inner peripheral face of the outer cylinder (2, 102); a carrier (4, 104) which is housed inside the outer cylinder (2, 102); the carrier (4, 104) being configured to be fixed to the other one of the partner members; a crank shaft (8, 108) which includes a shaft part (8b, 108b) rotatably supported by the carrier (4, 104) and a plurality of eccentric parts (8a, 108a) which are decentered relative to the shaft part (8b, 108b); a plurality of oscillating gears (10, 110) which include through-holes (10c, 110c) of a size, in which the eccentric parts (8a, 108a) of the crank shaft (8, 108) is configured to be inserted therethrough, and external teeth engaging with the internal gear pin (3, 103), and which are supported by the carrier (4, 104) so as to oscillate in conjunction with a rotation of the crank shaft (8, 108); and a plurality of roller bearings (18, 118) which are respectively provided to the plurality of eccentric parts (8a, 108a) of the crank shaft (8, 108), and support the oscillating gears (10, 110) so that they are relatively rotatable in relation to the eccentric parts (8a, 108a) of the crank shaft (8, 108) on an inner peripheral face of the through-holes (10c, 110c) of the oscillating gears (10, 110), and have rolling elements (18a, 118a) and a retainer (18b, 118b) which rollably retains the rolling element (18a, 118a) between the oscillating gear (10, 110) and the eccentric parts (8a, 108a); characterized in that the gear unit (1, 101) further comprises a washer (21, 71, 121) which is provided at a position where the washer (21, 71, 121) is able to come into contact with the retainer (18b, 118b) of the roller bearing (18, 118) provided to each of the adjacent eccentric parts (8a, 108a), and which regulates a movement of the roller bearing (18, 118) in an axial direction, and a housing recess (22, 72, 122) which houses the washer (21, 71, 121) is formed on at least one face among faces of the adjacent oscillating gears (10, 110) that face each other, the housing recess (22, 72, 122) includes an axial direction regulating surface (22a, 73a, 74a, 122a) which comes into contact with the washer (21, 71, 121) from the axial direction of the crank shaft (8, 108) and regulates movement of the washer (21, 71, 121) in the axial direction, and a radial direction regulating surface (22b, 73b, 74b, 122b) which comes into contact with an outer peripheral surface of the washer (21, 71, 121) and regulates movement of the washer (21, 71, 121) in a radial direction. an outer cylinder (2, 102) configured to be fixed to one of the partner members; a plurality of internal gear pins (3, 103) which are mounted on an inner peripheral face of the outer cylinder (2, 102); a carrier (4, 104) which is housed inside the outer cylinder (2, 102); the carrier (4, 104) being configured to be fixed to the other one of the partner members; a crank shaft (8, 108) which includes a shaft part (8b, 108b) rotatably supported by the carrier (4, 104) and a plurality of eccentric parts (8a, 108a) which are decentered relative to the shaft part (8b, 108b); a plurality of oscillating gears (10, 110) which include through-holes (10c, 110c) of a size, in which the eccentric parts (8a, 108a) of the crank shaft (8, 108) is configured to be inserted therethrough, and external teeth engaging with the internal gear pin (3, 103), and which are supported by the carrier (4, 104) so as to oscillate in conjunction with a rotation of the crank shaft (8, 108); and a plurality of roller bearings (18, 118) which are respectively provided to the plurality of eccentric parts (8a, 108a) of the crank shaft (8, 108), and support the oscillating gears (10, 110) so that they are relatively rotatable in relation to the eccentric parts (8a, 108a) of the crank shaft (8, 108) on an inner peripheral face of the through-holes (10c, 110c) of the oscillating gears (10, 110), and have rolling elements (18a, 118a) and a retainer (18b, 118b) which rollably retains the rolling element (18a, 118a) between the oscillating gear (10, 110) and the eccentric parts (8a, 108a); characterized in that the gear unit (1, 101) further comprises a washer (21, 71, 121) which is provided at a position where the washer (21, 71, 121) is able to come into contact with the retainer (18b, 118b) of the roller bearing (18, 118) provided to each of the adjacent eccentric parts (8a, 108a), and which regulates a movement of the roller bearing (18, 118) in an axial direction, and a housing recess (22, 72, 122) which houses the washer (21, 71, 121) is formed on at least one face among faces of the adjacent oscillating gears (10, 110) that face each other, the housing recess (22, 72, 122) includes an axial direction regulating surface (22a, 73a, 74a, 122a) which comes into contact with the washer (21, 71, 121) from the axial direction of the crank shaft (8, 108) and regulates movement of the washer (21, 71, 121) in the axial direction, and a radial direction regulating surface (22b, 73b, 74b, 122b) which comes into contact with an outer peripheral surface of the washer (21, 71, 121) and regulates movement of the washer (21, 71, 121) in a radial direction.