  We predict a new type of the negative-$U$ Anderson impurity formed in a
triple quantum dot. The two dots of the system behave as a negative-$U$
impurity preferring zero or double electron occupancy rather than single
occupancy, and the third dot stabilizes the attractive interaction of $U < 0$
via Coulomb repulsion. Using a bosonization method, we find that the system has
the two different phases of massive or vanishing charge fluctuations between
the two occupancies at low temperature, which are equivalent with the
antiferromagnetic and ferromagnetic phases of the anisotropic Kondo model,
respectively. The phase transition is experimentally accessible and
identifiable by electron conductance, offering the possibility of
experimentally exploring the anisotropic Kondo model.
