  We report the results of our spectrophotometric monitoring campaign for
AT~2017be in NGC~2537. Its lightcurve reveals a fast rise to an optical
maximum, followed by a plateau lasting about 30 days, and finally a fast
decline. Its absolute peak magnitude ($M_{r}$ $\simeq$ $-$12 $\rm{mag}$) is
fainter than that of core-collapse supernovae, and is consistent with those of
supernova impostors and other Intermediate-Luminosity Optical Transients. The
quasi-bolometric lightcurve peaks at $\sim$ 2 $\times$ 10$^{40}$ erg s$^{-1}$,
and the late-time photometry allows us to constrain an ejected $^{56}$Ni mass
of $\sim$ 8 $\times$ 10$^{-4}$\msun. The spectra of AT~2017be show minor
evolution over the observational period, a relatively blue continuum showing at
early phases, which becomes redder with time. A prominent H$\alpha$ emission
line always dominates over other Balmer lines. Weak Fe {\sc ii} features,
Ca~{\sc ii} H$\&$K and the Ca {\sc ii} NIR triplet are also visible, while
P-Cygni absorption troughs are found in a high resolution spectrum. In
addition, the [Ca~{\sc ii}] $\lambda$7291,7324 doublet is visible in all
spectra. This feature is typical of Intermediate-Luminosity Red Transients
(ILRTs), similar to SN~2008S. The relatively shallow archival Spitzer data are
not particularly constraining. On the other hand, a non-detection in deeper
near-infrared HST images disfavours a massive Luminous Blue Variable eruption
as the origin for AT~2017be. As has been suggested for other ILRTs, we propose
that AT~2017be is a candidate for a weak electron-capture supernova explosion
of a super-asymptotic giant branch star, still embedded in a thick dusty
envelope.
