This paper examines how the rules and the method for the employment adjustment (koyochosei) formed right after the Second World War in Japan. We focused on a case of the Showadenko Company which it could be clear to know the strategy of personnel retrenchment (jininseiri). The results of examination are as follows: First, the rules for an employment adjustment at the Showadenko Company were undoubtedly cleared in 1949. Those rules based on the ``work ability (gyomunoryoku),`` which included age, length of service, and work performance, that employees have to accept. We also need to pay attention that the union understood the rule of ``near fifty,`` which the management suggested, related to the retirement age. In 1949, the great transformation in the rules for an employment adjustment of the Showadenko Company was occurred. Second, the management of the Showadenko Company conducted the ``voluntary retirement (jihatsutaishoku)`` and paid ``retire-allowance (taishokukin)`` and ``extra-wage (rinjikyuyokin)`` in order to reduce friction between the management and the employees. The management also made the promise to do not repeatedly personnel retrenchment and do consultation prior to turnover. We can see the framework of the Japan`s employment adjustment method which was mentioned that it was established after the high-performance period.