  We report the first detection of the magnetic field in a star of FS CMa type,
a subgroup of objects characterized by the B[e] phenomenon. The split of
magnetically sensitive lines in IRAS 17449+2320 determines the magnetic field
modulus of 6.2+/-0.2 kG. Spectral lines and their variability reveal the
presence of a B-type spectrum and a hot continuum source in the visible. The
hot source confirms GALEX UV photometry. Because there is a lack of spectral
lines for the hot source in the visible, the spectral fitting gives only the
lower temperature limit of the hot source, which is 50 000 K, and the upper
limit for the B-type star of 11 100 K. The V/R ratio of the H alpha line shows
quasiperiodic behavior on timescale of 800 days. We detected a strong
red-shifted absorption in the wings of Balmer and OI lines in some of the
spectra. The absorption lines of helium and other metals show no, or very
small, variations, indicating unusually stable photospheric regions for FS CMa
stars. We detected two events of material infall, which were revealed to be
discrete absorption components of resonance lines.
  The discovery of the strong magnetic field together with the Gaia
measurements of the proper motion show that the most probable nature of this
star is that of a post-merger object created after the leaving the binary of
the birth cluster. Another possible scenario is a magnetic Ap star around
Terminal-Age Main Sequence (TAMS). On the other hand, the strong magnetic field
defies the hypothesis that IRAS 17449+2320 is an extreme classical Be star.
Thus, IRAS 17449+2320 provides a pretext for exploring a new explanation of the
nature of FS CMa stars or, at least, a group of stars with very similar
spectral properties.
