The invention relates to a device for dividing a light beam into two partial beams with a polarisation beam divider (4) with polarising layer which breaks an incident polarised light beam (1) down into a beam component reflected from the polarising layer (5) as a first partial beam (1) and a beam component allowed to pass in the direction of a beam axis (9), depending on the direction of polarisation. A phase transformer (16) and a mirror (17) are fitted downstream of the polarisation beam divider (4) along the beam axis (9). On the passage of the beam component (20) allowed through, the phase transformer (16) transforms the linear polarisation into a circular polarisation. The circularly polarised beam component (20) is reflected from the mirror (17). On the passage of the beam component (20) reflected by the mirror (17), the phase transformer (16) produces a 90 DEG phase shift in the polarisation and the beam component (20) once more impinging upon the polarisation beam divider (4) is totally reflected from the polarising layer (5) as the second partial beam (2).
