To provide a memory element at a large capacity, which can miniaturize a device with the simple structure and which can read and write with the electric signal, by providing a storage medium, which has the specified structure, on a board.

A memory element has the storage medium, which has a structure unit expressed with formula I, on a board. In the formula I, R1 is expressed with formula II, and R2 means a divalent organic group, and (n) means a numeric among 1-1000. In the formula II, R4, R5 mean hydrogen or organic group. Movement of the electron is generated in the compound by a voltage change, and the structure of the compound is changed to the structure of radical ion having absorption at 400-750nm so as to generate a color change, and unpaired electron is generated so as to change the electrical resistance. This change is utilized for memory element, for example, by providing an electrode on the storage medium between the board and the storage medium. Desirably, a writing electrode and a reading electrode are provided on the storage medium between the storage medium and the board.