A fixing device is provided. The fixing device is fixed to a surface, comprising a sucker, a rack, a gear, a transforming unit and a limiting unit. The rack is connected to the sucker. The gear is engaged to the rack. The transforming unit is connected to the gear. The transforming unit rotates the gear to move the rack between a first position and a second position. The rack pushes the sucker to apply a suction force to the surface when the rack is in the first position, and the suction force of the sucker is released when the rack is in the second position. The limiting unit is connected to the rack to restrict the rack.