PURPOSE: To enable the milling on the same surface with a protruding edge strip by forming a stopper device for a trimmer by two independent guide members arranged in parallel to a milling shaft on both sides of the milling shaft and guiding the trimmer along the flat surface of a semi-finished product plate.

CONSTITUTION: A plate-shaped semi-finished product 6 is composed of a flat surface 7 and a narrow-breadth surface 29 vertical to the surface 7, and an edge strip 5 is glued onto the surface 29. A narrow-breadth surface 30 vertical to the surface 29 has an S-shaped profile. In the milling of the projected edge strip 5, a trimmer 1 is guided by a retreating guide member 9 on the surface 7 of a semi-finished product, and a stopper mechanism 10 is guided to a scanning roller 12 and the edge strip vertical to the roller 12. A front guide member 9' is lifted from the surface 7. When a milling tool 4 reaches the narrow-breadth surface 30, the scanning roller 12 follows the S-shaped profile, and the trimmer 1 is guided by the guide member 9 and the stopper mechanism 10.