PURPOSE: To reduce a load on application software by adding a display permit level selecting means which selects a display permit level to a display control part and displaying only a character string having the display permit level indicated by said selecting means.

CONSTITUTION: The display control part 4 outputs screen data to a display part 5 according to the contents of attributes (ATR) 0 and 1 in the 1st and the 2nd buffers 31 and 32 and a display part 5 displays the characters of the screen data on the display. For example, a display permit bit (PMT) as one bit in an ATR is 1 and a key is inserted into the key switch 101 of a display permit level selection part 10 to send out a display permit signal to a control part 4. Then, a PMT selecting circuit 41 is actuated and a corresponding character string in the 1st buffer 31 is displayed according to the bits of the ATRs 0 and 1. When no key is inserted into the key switch 101 even if the PMT bit is 1, the corresponding character string is not displayed. Therefore, a person who has the key and a general operator who does not have the key, and display data are displayed selectively.