An aligning device is used for aligning a guide rail of an elevator system. The guide rail is held on a shaft wall of an elevator shaft and is displaceable in at least two horizontal directions, oriented crosswise with respect to each other, before a final fixation. The aligning device has a detection device that is configured to detect, in an automated manner, a position deviation of the guide rail from a nominal position, and has a hammer mill that is configured to hammer the guide rail in an automated manner depending on the detected position deviation by exerting pulse-like strikes in one of the horizontal directions toward the nominal position.