The invention discloses a gear milling machine used for machining a straight cone gear. The machine comprises a mounting base, a mounting plate is arranged on the upper portion of the mounting base ina sliding manner, one side of the mounting plate is provided with an air cylinder fixedly connected with the mounting base, an L-shaped connecting plate is perpendicularly welded to the position above the end, close to the air cylinder, of the mounting plate, the side, away from the air cylinder, of the L-shaped connecting plate is perpendicularly provided with a movable plate in a sliding manner, the movable plate is perpendicularly sleeved with a rotating shaft, the end, close to the mounting plate, of the rotating shaft is fixedly sleeved with a round-table-shaped rotating disc, driving levers are welded to the outer ring of the rotating disc in the axis line direction at equal distances, a positioning column is welded to the position above the mounting plate, the end, away from the air cylinder, of the mounting plate is perpendicularly welded with a supporting column, and the side, close to the mounting plate, of the supporting column is welded with an inclined guide plate. The gear which is preliminarily machined is automatically and rapidly subjected to chamfering and edge trimming operation, the gear machining efficiency is improved, manpower and material resources are saved, the gear surface is smooth and free of burrs, and the gear quality and attractiveness are improved.