To provide a more robust control of a rotary laser for changing from rotating operating mode to scanning operating mode.

A rotary laser includes: a laser beam unit 7 which is suitable for emitting at least one laser beam 2 rotating in a beam plane E and which is controlled by computer 9 so as to be switchable from a rotating operating mode I in which the at least one laser beam 2 rotates in the beam plane E, to a scanning operating mode II in which the at least one laser beam 2 scans in the beam plane E within an angular sector ; and a plurality of detectors 10 distributed circumferentially around an axis of rotation A, which are sensitive to an amplitude at least within the beam plane E and are connected to the computer 9.