To provide a laser beam machining method capable of machining a material layer located in the middle of a material with a high degree of accuracy into a voluntary shape and provide an encoder slit formed thereby and an image display body.

The laser beam machining method is characterized by the feature that, toward a forming body composed of a first material layer 1 which is transparent to at least a laser beam L, a second material layer 2 provided in contact with the first material layer 1, and a third material layer 3 provided in contact with the second material layer 2, the laser beam L is irradiated from the direction of the first material layer 1 and only the second material layer 2 is formed into a voluntary shape by a high-speed evaporation of the second material layer 2.