Abstract: A machine tool system includes a machine tool and a marking apparatus. The marking apparatus can mark parts-data on workpiece parts at high speed, without occupying any tool mounting station and without having any limitation in the number, the sequence direction, the size and the type font of characters to be marked. A mount base (33) is fixedly attached to a frame (1) of the machine tool. A marking head (51) is mounted on the mount base (37) so as to be movable in the vertical direction. The marking head (51) is provided with a pneumatic stylus (77) movable horizontally both in the X- and Y-axis direction. A parts-data of dot matrix type can be engraved on the workpiece parts by moving the stylus (77) in the X- and Y-axis directions.

Abstract: A thin-film light emitting element in which the light color emitted from the light emitting element can be voluntary changed in accordance with an electric power source applied to the light emitting element by utilizing scattering, accumulation, and discharge of an electric charge in a gate layer disposed between active layers of the light emitting element.