In this study, the automated process planning system for end-milling operation is realized. This study considers to minimize the number of times of tool change and to determine the appropriate machining sequence in the process planning. In our previous process planning system, the machining sequence is calculated geometrically, based on the Total Removal Volume (TRV) and the machining regions split from TRV. However, it remains difficulty to determine the best machining sequence from the large number of the calculated machining sequences. The previous process planning systems also do not consider machining conditions in the determination of the appropriate machining sequence. First, our new process planning system generates the association chart of machining regions, which represents the geometrical constraints to determine machining sequence. According to the association chart, the candidates can be selected from the enormous candidates of the machining sequence. Subsequently, our new process planning system determines the best machining sequence under considering the machining conditions. The best machining sequence is determined to minimize the number of times of tool change. A case study was conducted to show the effectiveness of our new proposed process planning system, and the machining sequence was automatically determined based on the geometrical constraints considered in process planning and the machining conditions considered in operation planning.