  In this paper we report the results of high-resolution circular
spectropolarimetric monitoring of the Herbig Ae star V380 Ori, in which we
discovered a magnetic field in 2005. A careful study of the intensity spectrum
reveals the presence of a cool spectroscopic companion. By modelling the binary
spectrum we infer the effective temperature of both stars: $10500\pm 500$ K for
the primary, and $5500\pm500$ K for the secondary, and we argue that the high
metallicity ($[M/H] = 0.5$), required to fit the lines may imply that the
primary is a chemically peculiar star. We observe that the radial velocity of
the secondary's lines varies with time, while that of the the primary does not.
By fitting these variations we derive the orbital parameters of the system. We
find an orbital period of $104\pm5$ d, and a mass ratio ($M_{\rm P}/M_{\rm S}$)
larger than 2.9. The intensity spectrum is heavily contaminated with strong,
broad and variable emission. A simple analysis of these lines reveals that a
disk might surround the binary, and that a wind occurs in the environment of
the system. Finally, we performed a magnetic analysis using the Least-Squares
Deconvolved (LSD) profiles of the Stokes $V$ spectra of both stars, and
adopting the oblique rotator model. From rotational modulation of the primary's
Stokes $V$ signatures, we infer its rotation period $P=4.31276\pm0.00042$ d,
and find that it hosts a centred dipole magnetic field of polar strength
$2.12\pm0.15$ kG, with a magnetic obliquity $\beta = 66\pm5^{\circ}$, and a
rotation axis inclination $i=32\pm5^{\circ}$. However, no magnetic field is
detected in the secondary, and if it hosts a dipolar magnetic field, its
strength must be below about 500 G, to be consistent with our observations.
