A planetary gear device includes: a sun gear having external teeth; a plurality of planet gears having external teeth and meshed with the sun gear; a ring gear having internal teeth and meshed with the planet gears; and a baffle unit disposed between the planet gears adjacent to each other and configured to collect lubricant oil into a collection chamber. The baffle unit includes: a discharge outlet to discharge a portion of the lubricant oil collected in the collection chamber in an axial direction; and a ring gear oil supply hole to discharge another portion of the lubricant oil in a radially outward direction and supplied to the ring gear, and a weir member separable from the baffle unit and configured to cover a portion of the discharge outlet to reserve the lubricant oil to be discharged through the ring gear oil supply hole.
