Rotational construction laser

The device (31) has a laser (33) and a deflecting unit including pentagonal prism (50), which is motor-driven about a rotation axis. The deflecting unit projects over the device casing (32) and has an additional window (53). A detection unit for light reflected from a reference mark is connected to an evaluation and control unit, which control a tilt device (37), to tilt the rotation axis of the deflection device. Automatically-controlled positioning units (40) are provided, to adjust the axial position of deflecting unit according to the position of the reflection from the reference mark.