  We analyze a generalized Dirac system, where the dispersion along the $k_{x}$
and $k_{y}$ axes is $N$-th power and linear along the $k_{z}$ axis. When we
apply magnetic field, there emerge $N$ monopole-antimonopole pairs beyond a
certain critical field in general. As the direction of the magnetic field is
rotated toward the $z$ axis, monopoles move to the north pole while
antimonopoles move to the south pole. When the magnetic field becomes parallel
to the $z$ axis, they merge into one monopole or one antimonopole whose
monopole charge is $\pm N$. The resultant system is a multiple-Weyl semimetal.
Characteristic properties of such a system are that the anomalous Hall effect
and the chiral anomaly are enhanced by $N$ times and that $N$ Fermi arcs
appear. These phenomena will be observed experimentally in the cubic-Dirac and
triple-Weyl fermion systems ($N=3$).
