Candidate character strings representing objects disposed in a work cell, models for robot operation instructions which has variable parts, and robot commands related to the objects are defined in advance. By inputting a query such as `Workpiece 1 ?` by voice, the object concerned is indicated by a display color so that the work cell can be confirmed. Models for operation instructions and a program to be edited are displayed to allow an operator to select the portion to be edited. When an operation instruction is input by voice in the model pattern, candidate character strings are assigned to the variable parts of the model. A completed statement that matches the voice-recognized statement is found, the robot operation commands defined for the objects are displayed, and the robot operation is displayed on the screen. The operation commands are inserted at the desired location in the program.