A swing arm structure for a saddle riding type vehicle, the saddle riding type vehicle including a vehicle body frame and a swing arm supported vertically swingably on the vehicle body frame, the swing arm structure comprising: a pivot shaft (41, 42) disposed in the vehicle body frame, the pivot shaft (41, 42) extending in a lateral direction of the vehicle; a pair of wall portions (8L, 8R) disposed in the lateral direction of the vehicle in one of the vehicle body frame and the swing arm; and an interposed portion disposed between the wall portions (8L, 8R) in the other of the vehicle body frame and the swing arm, wherein at least one of the wall portions (8L, 8R) has a wall portion-side pass-through portion (43h, 44h) formed therein, the wall portion-side pass-through portion (43h, 44h) receiving the pivot shaft (41, 42) passed therethrough, the interposed portion has an interposed portion-side pass-through portion (45h, 46h) formed therein at, out of both lateral end portions, a portion facing the wall portion-side pass-through portion (43h, 44h), the interposed portion-side pass-through portion (45h, 46h) receiving the pivot shaft (41, 42) passed therethrough, the interposed portion has a non-pass-through portion formed therein at least at a lateral middle portion of the interposed portion, the non-pass-through portion not receiving the pivot shaft (41, 42), the wall portions (8L, 8R) are disposed in the vehicle body frame, the interposed portion is disposed in the swing arm, the interposed portion has an interposed portion-side pass-through portion forming portion (45, 46) in which the interposed portion-side pass-through portion (45h, 46h) is formed, the pivot shaft (41, 42) is rotatably supported by a bearing (40, 55) disposed between the pivot shaft (41, 42) and the interposed portion-side pass-through portion forming portion (45, 46), one of an inner ring and an outer ring that constitute the bearing is fixed in one of the pivot shaft and the interposed portion-side pass-through portion forming portion, and the other of the inner ring and the outer ring is fixed in the other of the pivot shaft and the interposed portion-side pass-through portion forming portion; characterized in that the swing arm structure further comprises a nut member threadedly engageable with the pivot shaft, wherein the nut member is disposed in a hollow portion that forms the interposed portion-side pass-through portion in the swing arm, the inner ring is fixed through threaded engagement of the nut member with the pivot shaft, and the outer ring is fixed to the interposed portion-side pass-through portion forming portion. a pivot shaft (41, 42) disposed in the vehicle body frame, the pivot shaft (41, 42) extending in a lateral direction of the vehicle; a pair of wall portions (8L, 8R) disposed in the lateral direction of the vehicle in one of the vehicle body frame and the swing arm; and an interposed portion disposed between the wall portions (8L, 8R) in the other of the vehicle body frame and the swing arm, wherein at least one of the wall portions (8L, 8R) has a wall portion-side pass-through portion (43h, 44h) formed therein, the wall portion-side pass-through portion (43h, 44h) receiving the pivot shaft (41, 42) passed therethrough, the interposed portion has an interposed portion-side pass-through portion (45h, 46h) formed therein at, out of both lateral end portions, a portion facing the wall portion-side pass-through portion (43h, 44h), the interposed portion-side pass-through portion (45h, 46h) receiving the pivot shaft (41, 42) passed therethrough, the interposed portion has a non-pass-through portion formed therein at least at a lateral middle portion of the interposed portion, the non-pass-through portion not receiving the pivot shaft (41, 42), the wall portions (8L, 8R) are disposed in the vehicle body frame, the interposed portion is disposed in the swing arm, the interposed portion has an interposed portion-side pass-through portion forming portion (45, 46) in which the interposed portion-side pass-through portion (45h, 46h) is formed, the pivot shaft (41, 42) is rotatably supported by a bearing (40, 55) disposed between the pivot shaft (41, 42) and the interposed portion-side pass-through portion forming portion (45, 46), one of an inner ring and an outer ring that constitute the bearing is fixed in one of the pivot shaft and the interposed portion-side pass-through portion forming portion, and the other of the inner ring and the outer ring is fixed in the other of the pivot shaft and the interposed portion-side pass-through portion forming portion; characterized in that the swing arm structure further comprises a nut member threadedly engageable with the pivot shaft, wherein the nut member is disposed in a hollow portion that forms the interposed portion-side pass-through portion in the swing arm, the inner ring is fixed through threaded engagement of the nut member with the pivot shaft, and the outer ring is fixed to the interposed portion-side pass-through portion forming portion.