PURPOSE: To provide the command entry device in which a help function is easily added to an existing program and by which an optimum message to each operator is selected.

CONSTITUTION: The input aid device receiving a command requiring an option and a parameter with an entry means 1 and giving the command to a command execution means 3 consists of a command entry aid information file 5 storing each command, a regular option and help information relating to the regular option with cross reference, an aid information edit means 4 editing the content of the command entry aid information file 5, a command entry aid means 6 selecting the option while displaying the help information on a display means 2 based on the content of the command entry aid information file 5, and a command generating means 7 converting data entered from the command entry aid means 6 into a regular command and its option.