An offline teaching apparatus including a data acquiring section for acquiring position and orientation data and processing-condition data including interpolation commands, at respective predefined taught points, from an existing first processing program for a first workpiece; a processing-path calculating section for determining a processing path in the first program, based on the position and orientation data and the interpolation commands; a model generating section for generating, by using data of a second workpiece model of a second workpiece having geometrical features different from the first workpiece, a processing line showing a range of processing on the second workpiece; a taught-point calculating section for determining a geometrical correlation between the processing path and the processing line, and determining positions and orientations at respective taught points in the processing line; and a program generating section for generating a processing program for the second workpiece, by using the processing-condition data at the predefined taught points as well as the positions and the orientations at the taught points.