Pathria's approach has been used to deal with the properties of the finite cubic system of [sup 4]He under constant pressure. The analytic expressions for the total number of particles [ital N] and the total pressure [ital p] near the critical point are obtained for mixture, antiperiodic, Neumann, and periodic boundary conditions. Influences of various boundary conditions upon low-temperature and critical characters of finite systems are discussed. For five boundary conditions, the relationship between the superfluid transition temperature [ital T][prime] and the size of the finite system [ital L][sub 0] has been obtained. The results of this paper can be used in the case of superconductivity. Besides, from this work and others, we have obtained the formula for the phase-transition temperature [ital T][prime] in a finite system, [ital t]=[sigma][ital L][sub 0][sup [minus][ital b]]; here [ital b] is described as the finiteness constant, and [sigma] is determined by the boundary conditions, the properties of the system, and the interaction between the system and the walls of the container.