  In this Letter the bound states of (2+1) Dirac equation with the
cylindrically symmetric $\delta (r-r_{0})$-potential are discussed. It is
surprisingly found that the relation between the radial functions at two sides
of $r_{0}$ can be established by an SO(2) transformation. We obtain a
transcendental equation for calculating the energy of the bound state from the
matching condition in the configuration space. The condition for existence of
bound states is determined by the Sturm-Liouville theorem.
