We calculate physical quantities accompanying dynamical chiral symmetry breaking in QCD like theories. To emphasize the consistency of our approximation with chiral symmetry, we first derive an effective action for a bilocal auxiliary field standing for ψ(x)ψ(y), from which the Schwinger-Dyson equation for fermion self-energy Σ and the Bethe-Salpeter equation for the Nambu-Goldstone bound state follow. An expression for the decay constant (usually called fπ) is given exactly to the ladder approximation by solving the Bethe-Salpeter equation. Numerical calculation is done for Σ, fπ, ≪ψψ>R, with various β-functions of the gauge coupling constant. We find that fπ/≪ψψ>R, fπ/ΛQCD are rather stable against the infrared cutoff parameter, while Σ-function itself depends strongly on the infrared cutoff.