  We compare the accretion flow onto the neutron star induced by Roche lobe
overflow with that by the overflow from the Be disk, in a zero eccentricity,
short period binary with the same mass transfer rate, performing
three-dimensional Smoothed Particle Hydrodynamics simulations. We find that a
persistent accretion disk is formed around the neutron star in both cases. The
circularization radius of the material transferred via Roche lobe overflow is
larger than that of the material transfered from the Be disk. Thus, the growth
of the accretion disk in the former case becomes significantly slower than in
the latter case. In both cases, the mass accretion rate is very small and
varies little with orbital phase, which is consistent with the observed X-ray
behaviour of Be/X-ray binaries with circular orbits (e.g. XTE J1543-568).
