1. A handwriting input/output system comprising: a medium that comprises a writing area, on at least part of or a plurality of areas of the medium, formed with a dot pattern that repeatedly defines coordinate information and code information; an imaging unit that images the dot pattern of the writing area and transmits image data thereof; a dot pattern analysis unit that stores the image data of the dot pattern imaged and transmitted from the imaging unit into a storage element and analyzes a code of the image data to obtain trajectory information including the coordinate information and the code information; a trajectory recognition unit that recognizes the trajectory information of a letter, a character, and/or a figure that is traced on a surface of the writing area based on a change in the analyzed coordinate information; and a process instruction unit that transmits a process instruction and the trajectory information according to recognized recognition information to an information processing unit.