The condition of the possibility for the boundary contact integrals regularization in two-dimensional problems of acoustic is considered. On an example of the simplest boundary contact problem of acoustics is shown, that the known sufficient condition of this possibility is necessary as well. The study of analytical properties of the transitional admittances of an infinite plate contacting with a medium are carried out for obtaining this statement. The reviewings are carried out in the common terms, so the results are suitable for arbitrary used models of plates theory and can be adapted to boundary contact problems of other physical nature.