The invention relates to a gear apparatus. The gear apparatus according to the present disclosure includes: a sun gear; a carrier to which planetary gear shafts rotatably supporting multiple planetarygears meshing with this sun gear are fixed; an external gear portion; a gear cylinder having an internal gear portion meshing with the planetary gears; a gear meshing with the external gear portion of the gear cylinder; a lubricating oil passage formed in the planetary gears shafts, the lubricating oil passage configured to supply the lubricating oil to respective mashing parts between the planetary gears and the internal gear portion and between the planetary gears and the sun gear; and a lubricating oil guiding passage having one end opening to an inner circumferential surface of the gear cylinder, and discharging the lubricating oil present on an inner circumferential surface of the gear cylinder toward the meshing part between the external gear portion and the gear.