It is an object of the present invention to improve visibility for observation with naked eyes or for camera shooting without spoiling the appearance during marking inside a. transparent medium using a laser. By irradiating an inside of a transparent medium with a laser, the present invention forms a micro-denatured region in each of a first layer and a second layer inside the medium. The micro-denatured regions in the respective layers are arranged out of alignment with each other on a two-dimensional plane (refer to FIG. 1).

It is an object of the present invention to improve visibility for observation with naked eyes or for camera shooting without spoiling the appearance during marking inside a transparent medium using a laser. By irradiating an inside of a transparent medium with a laser, the present invention forms a micro-denatured region in each of a first layer and a second layer inside the medium. The micro-denatured regions in the respective layers are arranged out of alignment with each other on a two-dimensional plane (refer to FIG. 1).