PURPOSE: To simplify program teaching of marking operation by holding a marker by a holding mechanism to move back and forth in the direction toward the outside surface of a work and energizing the marker by an energizing mechanism to the outside surface of the work.

CONSTITUTION: A marker 6 is set at a position near the outside surface 7a of the work 7 when the command of a marking operation is outputted from a controlling device and the marker 6 is released from pressing by an elbow part 10b when a fixing piece 10a is moved clockwise by motion of a driver 10c. The marking operation by a robot is performed according to a program. A required marking operation is performed by only a movement of a working part 5 on a specified plane space faced the outside surface 7a, even when the surface 7a is curved or uneven, because the marker 6 is energized to the outside surface 7a.