To easily prepare the program of a similar work based on a basic robot program used in actual site.

This basic robot program 30P is described in coordinate position data Rs, Re on a robot coordinate system. By using the coordinate position of a similar work on a work coordinate as a variable, a conversion program Fn to convert the variable to a difference of the coordinate position on the robot coordinate system is prepared. When the coordinate position data of a basic work and the similar work on the work coordinate system is substituted in the conversion program Fn, the difference of the coordinate position on the robot coordinate system is calculated, the coordinate positions Rs, Re of the basic work described by the robot coordinate system in the basic robot program 30P are shifted by the amount of the calculated difference, and the shifted coordinate positions Rs', Re' on the robot coordinate system can be obtained. Thus a robot program 30Q suitable for the similar work can be prepared.