A planetary gear device comprising: a sun gear having external teeth; a plurality of planet gears that have external teeth and mesh with the sun gear; a ring gear that has internal teeth and meshes with the planet gears; and a baffle unit (5, 5A-D) disposed in a circumferential gap defined between the planet gears adjacent to each other, the baffle unit (5, 5A-D) including: a first introduction opening portion that is open in a radially inward direction, and configured to introduce lubricating oil, which has lubricated tooth surfaces of the sun gear and the planet gears, into the baffle unit (5, 5A-D); a radially outer end wall that is disposed in the vicinity of a radially inner side of the ring gear; an end wall disposed at one end portion of the radially outer end wall and forming one end, in an axial direction, of the first introduction opening portion; a discharge opening portion to discharge the lubricating oil in the baffle unit (5, 5A-D); and a guide portion (27A, 27B) disposed at least at a side portion of the baffle unit (5, 5A-D) on a rear side in a rotation direction of the sun gear, and configured to cover the first introduction opening portion in the circumferential direction, and to guide the lubricating oil into the first introduction opening portion, a housing or a rotary shaft of the sun gear has a supply opening to supply the lubricating oil to the tooth surface of the sun gear, characterized in that a circumferential width of the first introduction opening portion is set so as to be greater than a minimum gap between two planet gears adjacent to each other. a sun gear having external teeth; a plurality of planet gears that have external teeth and mesh with the sun gear; a ring gear that has internal teeth and meshes with the planet gears; and a baffle unit (5, 5A-D) disposed in a circumferential gap defined between the planet gears adjacent to each other, the baffle unit (5, 5A-D) including: a first introduction opening portion that is open in a radially inward direction, and configured to introduce lubricating oil, which has lubricated tooth surfaces of the sun gear and the planet gears, into the baffle unit (5, 5A-D); a radially outer end wall that is disposed in the vicinity of a radially inner side of the ring gear; an end wall disposed at one end portion of the radially outer end wall and forming one end, in an axial direction, of the first introduction opening portion; a discharge opening portion to discharge the lubricating oil in the baffle unit (5, 5A-D); and a guide portion (27A, 27B) disposed at least at a side portion of the baffle unit (5, 5A-D) on a rear side in a rotation direction of the sun gear, and configured to cover the first introduction opening portion in the circumferential direction, and to guide the lubricating oil into the first introduction opening portion, a first introduction opening portion that is open in a radially inward direction, and configured to introduce lubricating oil, which has lubricated tooth surfaces of the sun gear and the planet gears, into the baffle unit (5, 5A-D); a radially outer end wall that is disposed in the vicinity of a radially inner side of the ring gear; an end wall disposed at one end portion of the radially outer end wall and forming one end, in an axial direction, of the first introduction opening portion; a discharge opening portion to discharge the lubricating oil in the baffle unit (5, 5A-D); and a guide portion (27A, 27B) disposed at least at a side portion of the baffle unit (5, 5A-D) on a rear side in a rotation direction of the sun gear, and configured to cover the first introduction opening portion in the circumferential direction, and to guide the lubricating oil into the first introduction opening portion, a housing or a rotary shaft of the sun gear has a supply opening to supply the lubricating oil to the tooth surface of the sun gear, characterized in that a circumferential width of the first introduction opening portion is set so as to be greater than a minimum gap between two planet gears adjacent to each other.