  The z-transform technique is used to investigate the model for distribution
of high-tax payers, which is proposed by two of the authors (K. Y and S. M) and
others. Our analysis shows an asymptotic power-law of this model with the
exponent -5/2 when a total ``mass'' has a certain critical value. Below the
critical value, the system exhibits an ordinary critical behavior, and scaling
relations hold. Above the threshold, numerical simulations show that a
power-law distribution coexists with a huge ``monopolized'' member. It is
argued that these behaviors are observed universally in conserved aggregation
processes, by analizing an extended model.
