  We report the discovery of the bright reflected emission component in the
super-Eddington state of the ULX pulsar Swift J0243.6+6124, based on the NuSTAR
observations of the source during its 2017 outburst. The flux of the reflected
emission is weakly variable over the pulsar phase while the direct emission
shows significantly larger pulsation amplitude. We propose that in this system
the neutron star finds itself in the centre of the well formed by the inner
edge of the geometrically thick super-Eddington accretion disc truncated by the
magnetic field of the pulsar. The aspect ratio of the well is H/R \sim 1. The
inner edge of the truncated disc is continuously illuminated by the emission of
the accretion column giving rise to the weakly variable reflected emission. As
the neutron star rotates, its emission sweeps through the line of sight, giving
rise to the pulsating direct emission. From Doppler broadening of the iron
line, we measure the truncation radius of the accretion disc \sim 50 R_g. The
inferred dipole component of the magnetic field is consistent with previous
estimates favouring a not very strong field. The uniqueness of this system is
determined by its moderately super-Eddington accretion rate and the moderate
magnetic field so that the inner edge of the truncated geometrically thick
accretion disc is seen from the neutron star at a large solid angle.
