This paper proposes a method for solving congestion management problem by optimally allocating FACTS devices. The problem is approached by utilizing optimization method which optimizes generation and installation costs while satisfying voltage stability index. The main contribution of this paper is to provide pareto optimal solutions which describe previous objectives during congestion and after congestion removed. Moreover, the method is able to rank optimal location in relieving congestion, to describe feasibility of solutions and to show better solution in improving voltage stability. Therefore, it is valuable for decision maker in determining locations and sizes of devices which gaining the benefit. Due to the complexity of the problem, Multi Objective Particle Swarm Optimization (MOPSO) is utilized to optimize devices allocation as master sub-problem; Sequential Quadratic Programming (SQP) is used to solve the operation sub-problem, and Point of Collapse method is applied to calculate load margin during contingency. The effectiveness of this technique is demonstrated in modified IEEE 14 bus system.