Numerical controller with function to add display screens

A numerical controller which has a function to add display screens, wherein

• said numerical controller comprises:
• a display unit;
• a memory device stored with display means which causes the display unit to display a standard display screen;
• and
• a detachable external memory device stored with additional display screen data to be displayed as an additional display screen on the display unit, and wherein
• said display means includes:
• attachment/detachment determining means which determines whether or not the external memory device is attached to the numerical controller;
• storage determining means which determines whether or not the external memory device is stored with the additional display screen data;
• and
• selection display means which selects and displays the standard display screen and/or the additional display screen on the display unit based on results of the determination by the attachment/detachment determining means and the storage determining means.