  NA61/SHINE is an experiment at the CERN Super Proton Synchrotron. The main
goals of the experiment are the search for the critical point of strongly
interacting matter and the study of the properties of the onset of
deconfinement. To reach these goals, the two-dimensional scan in beam momentum
($13A-150A$ GeV/$c$) and system size ($p$+$p$, Be+Be, Ar+Sc, Xe+La, Pb+Pb) was
performed. In the final stage of the collision, the spectra of protons are only
weakly affected by the effects of resonance decays and rescattering due to
their large mass. Thus, proton rapidity distribution is particularly sensitive
to the onset of deconfinement. This article presents experimental results on
proton production in the collision energy range, which is most relevant to the
onset of deconfinement. The procedure of measuring the proton rapidity spectra
by NA61/SHINE is described, as well as Collaboration's recent results from
reactions of $p$+$p$, Be+Be and Ar+Sc. Presented experimental results are
confronted with existing data and models.
