  A non-subtractive recipe of Casimir energy renormalization efficient in the
presence of logarithmically divergent terms is proposed. It is demonstrated
that it can be applied even in such cases, when energy levels can be obtained
only numerically whereas neither their asymptotical behavior, nor the
analytical form of the corresponding spectral equation can be studied. The
results of numerical calculations performed with this method are compared to
those obtained by means of explicit subtraction of divergent terms from energy.
