<p>Provided is a planetary gear reduction device (1) equipped with: a sun gear (5) that is affixed concentric with respect to the input shaft for the motive power and has external teeth; multiple planet gears (7) that have external teeth and mesh with the aforementioned sun gear (5); a ring gear (9) that has internal teeth and meshes with the aforementioned planet gears (7); a planet gear (11) that supports he multiple planet shafts (13), which are the axes of rotation for each of the planet gears (7), and that outputs the orbital motion of the multiple planet gears (7) as first motive power; and a tubular support member (27) that is connected so as to be unable to rotate relative to the ring gear (9) and that outputs the rotation of the ring gear (9) as second motive power. A flexible structure (41) having a V-shaped vertical cross section that is recessed toward the inner diameter is provided at one location in the axial central direction of the tubular support member (27). Thus, rigidity can be ensured and misalignment can be prevented while limiting an increase in the weight of the device.</p>
