We consider the dynamical symmetry breaking in the quenched, planar version of quantum electrodynamics using the Schwinger-Dyson equation. In the study, we can find the region in which the mass of the fermion fields is dynamically generated. In the region, the scale symmetry is broken explicitly and the chiral symmetry is broken spontaneously. We investigate the critical behavior governed by the critical exponents. One of the critical exponents is calculated and the anomalous dimension is obtained by the results of the Schwinger-Dyson equation. We also obtain the effective potential which gives the same critical exponent and the same anomalous dimension.