1. A numerical control unit that controls a machine tool based on a machining program in which operation modes and operation commands to control a servo motor, a spindle motor, and a peripheral device constituting the machine tool are instructed, the numerical control unit comprising: a machining program analysis unit configured to analyze the machining program; an operation-mode-control execution unit configured to control the servo motor, the spindle motor, and the peripheral device based on the operation modes and the operation commands analyzed by the machining program analysis unit; an operation mode screen correspondence storage unit configured to store in advance the relations between an operation-mode-screen displaying operation conditions of the servo motor, the spindle motor, and the peripheral device prepared for each of the operation modes, and, operation mode; and an operation mode screen display unit configured to select the operation-mode-screen to be display, based on the operation mode screen relations, as a operation-mode-screen, corresponding to the operation mode currently being executed obtained by the operation mode control execution unit, and display the selected operation-mode-screen in a display.