An axial adjustment device includes: a main body; two slide seats disposed in the main body; a first and a second threaded rods disposed in the main body and respectively screwed in the two slide seats; a first transmission gear connected with the first threaded rod; a second transmission gear connected with the second threaded rod; and a fastening member. When the fastening member is switched to a fastening position, the two threaded rods are driven with each other via the two transmission gears. When the fastening member is switched to a releasing position, the two threaded rods can be only independently rotated. The axial adjustment device can control the two slide seats to independently or synchronously move.