A back gauge for a back gauge positioning system of a bending machine includes a stop finger on which at least one stop surface is configured, and a base unit that is configured for coupling with the back gauge positioning system. The stop finger is coupled with the base unit by a linear guide, and the stop finger can be displaced relative to the base unit between a pushed-forward working position and a retracted position. The stop finger and the base unit are coupled with a first spring element, by which the stop finger is pre-loaded into its working position, and a locking device is configured, by which the stop finger can optionally be locked in the working position or is released into its retracted position for displacement counter to the spring force of the first spring element.