An automatic paper feeding mechanism adapted to a paper roll is disclosed. The automatic paper feeding mechanism includes a first pivotal member, a paper pressing module, a driving member and a paper guiding module. The paper pressing module is pivoted to the first pivotal member for pressing the paper roll. The driving member is for driving the paper pressing module, such that the paper pressing module respectively presses the paper roll in a first position and a second position. The paper guiding module is connected to the paper pressing module. The paper guiding module is driven by the paper pressing module to move from a first guiding position to a second guiding position when the paper pressing module is moved from the first position to the second position, so as to adjust a gap between the paper guiding module and the paper roll.