  Cosmic rays are hampered by the Moon and a deficit in its direction is
expected (the so-called \emph{Moon shadow}). The Moon shadow is an important
tool to determine the performance of an air shower array. Indeed, the westward
displacement of the shadow center, due to the bending effect of the geomagnetic
field on the propagation of cosmic rays, allows the setting of the absolute
rigidity scale of the primary particles inducing the showers recorded by the
detector. In addition, the shape of the shadow permits to determine the
detector point spread function, while the position of the deficit at high
energies allows the evaluation of its absolute pointing accuracy.
  In this paper we present the observation of the cosmic ray Moon shadowing
effect carried out by the ARGO-YBJ experiment in the multi-TeV energy region
with high statistical significance (55 standard deviations). By means of an
accurate Monte Carlo simulation of the cosmic rays propagation in the
Earth-Moon system, we have studied separately the effect of the geomagnetic
field and of the detector point spread function on the observed shadow. The
angular resolution as a function of the particle multiplicity and the pointing
accuracy have been obtained. The primary energy of detected showers has been
estimated by measuring the westward displacement as a function of the particle
multiplicity, thus calibrating the relation between shower size and cosmic ray
energy. The stability of the detector on a monthly basis has been checked by
monitoring the position and the deficit of the Moon shadow. Finally, we have
studied with high statistical accuracy the shadowing effect in the
"day"/"night" time looking for possible effect induced by the solar wind.
