PURPOSE: To improve workability by previously storing guidance information, help information, or the like constituted of the information such as display positions, display characters from a host device to a storage means.

CONSTITUTION: Command information from the host device is inputted to a command data generating means 38 through an input data inputting means 40. The means 38 compares the guidance information number data of the inputted data with data stored in a command data storage means 39 storing guidance information 42 displayed on a display unit 6 at present, and when both the data are coincident with each other, a guidance information erasing command is sent to a screen display data selecting means 12. Receiving the command, the means 12 uses data stored in a screen display data storage means storing the (M+1)th display screen data for displaying the (M+1)th screen on the display unit 6 by a display unit driving means 10. Thereby, the displayed screen display data are left without being erased until an operator outputs a guidance information erasing command.