A pencil sharpener has a waste case, a blade base, a blocking chunk, a blade, a rotating knob and an adjusting shaft. The waste case has a mounting hole and multiple positioning segments formed on the inner wall of the mounting hole. The blocking chunk is moveably mounted on the bottom of the blade base along an axial direction of the blade base. The blade is mounted securely on the blade base. The rotating knob is mounted rotatably in the mounting hole in the waste case and has at least one engaging segment selectively engaging the positioning segments of the waste case. The adjusting shaft is connected securely with the rotating knob and is disposed on the blocking chunk. When the rotating knob is rotated, the adjusting shaft is rotated to push the blocking chunk to move along the axial direction of the blade base.