In the machine manufacturing industry, CNC machine tools possess many advantages and have gradually become the leading machine tools to replace the ordinary machine tools. According to their processing usages, they can be divided into two kinds: general CNC and NTC. With the automatic tool change device consisting of tool magazine and mechanical arm, the latter can complete the most, if not all, processings of workpieces in a clamping. According to the instruction to select tools from the digital control system, the tools in the tool magazine can be located to the position for tool change, which is called automatic tool selection. Automatical tool selection can be implemented at random and sequentially. This paper focuses on random tool selection in ATC tool magazine controlled by Mitsubishi FX2N PLC series.