Abstract: A pen containing multi-color cores located in different tubes housed in the pen body, which colors can be optionally selected for use readily using a specially-designed turnable knob having a projected edge in cam contact with the top end of the core-receiving tubes. The top end of the core-receiving tube is pushed downward for use, when the turnable knob is rotated, so to enable a person to select a color core as he wishes quickly and readily.