An injection mold for forming a light guide plate including a first block, a second block configured to face the first block, a forming portion included between the first and second blocks facing each other and having a shape of the light guide plate, an injection portion formed at the first block and configured to receive injected resin for forming the light guide plate, and a gate portion configured to guide the injected resin from the injection portion to the forming portion. Further, a width of a first end portion of the gate portion that is connected to the forming portion is 50%-80% of a width of the forming portion.