  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 then, when energy levels can be obtained only
numerically and neither their asymptotical behavior, nor the analytic form of
spectral equation is known. The results of calculations performed with this
method are compared to those obtained by means of explicit subtraction of
divergent terms from energy.
