  The weak antiferromagnetism of URu${}_{2}$Si${}_{2}$ is discussed on the
basis of a duality model which takes into account salient features of both
itinerant fermions and "localized" component of spin degrees of freedom. The
problem is analyzed in the framework of induced-moment mechanism by taking a
singlet-singlet crystal field scheme together with the nesting property of
partial Fermi surface of itinerant fermions . It is shown that the extremely
small ordered moment $m$ of ${\cal O}$($10^{-2}$$\times$$\mu_{B}$) can be
compatible with the large specific-heat jump at the transition temperature
$T_{N}$. Analysis performed in the presence of external magnetic field shows
that the field dependence of $m$ in the limit T\to 0 and T_{N}$ do not scale
except very near the critical field B which is consistent with a recent
observation by Mentink. It is also shown that the antiferromagnetic magnetic
order gives rise to a tiny amount of antiferromagnetic orbital order of
f-electrons.

Strongly Correlated Electrons