In this paper, regarding how we can make a privatized postal-services company continue implementing social purposes, we derive the objective conditions that can be also referred to the postal reforms in Japan by carrying out mutual comparison of the experiences in postal-privatization-advanced nations, such as Germany, Britain, and New Zealand. The first condition we derive is that management stability and development of a postal services company should be achieved after privatization, and the second is that effectual schemes should be prepared that the results of management stability and development would be distributed to the social purpose fulfillment. Although German postal services privatization fulfilled the first conditions to some extent, it failed to satisfy the second. Britain is conversely considered not fulfilling the first condition in spite of establishing an excellent scheme reflecting the demands of residents to the management of the British mail company. We can confirm the objectivities of these conditions by comparing them with the experiences in New Zealand. In addition, as important matters drawn from comparison of these three nations, in order to acquire the first conditions we ought to aim at liberalization policy introduction at suitable time, and as to the second condition we should secure its effectiveness.