Patent ID: 8199133

Claim:
A writing device comprising: a display medium comprising: a first display layer in which if a pulse voltage is applied to a part of the first display layer, a state of the part changes to a reflective state in which the part reflects light of a first wavelength of outside light or a light transmissive state in which the part transmits light of the first wavelength of outside light, depending on a value of the pulse voltage; a second display layer stacked on the first display layer, in which if a pulse voltage is applied to a part of the second display layer, a state of the part changes to a reflective state in which the part reflects light of a second wavelength, which is different from the first wavelength, of outside light or a light transmissive state in which the part transmits light of the second wavelength of outside light, depending on a value of the pulse voltage; a first conductive layer and a second conductive layer sandwiching the first display layer and the second display layer, to which bias voltage is applied from outside; and a photosensitive layer located between the first conductive layer and the second conductive layer such that upon irradiation of the photosensitive layer with light a value of a pulse voltage applied to the first display layer and the second display layer increases, wherein: a value of a pulse voltage for changing a state of the first display layer is different from a value of a pulse voltage for changing a state of the second display layer; a ratio of a pulse voltage applied to the first display layer via the first conductive layer and the second conductive layer and a pulse voltage applied to the second display layer via the first conductive layer and the second conductive layer changes depending a frequency of a bias voltage applied to the first conductive layer and the second conductive layer; and a value of a pulse voltage for changing a state of the first display layer and a value of a pulse voltage for changing a state of the second display layer change depending on a frequency of a bias voltage applied to the first conductive layer and the second conductive layer; a voltage-applying unit that applies a bias voltage to the first conductive layer and the second conductive layer, a frequency of the bias voltage differing between a case in which a state of the first display layer and a state of the second display layer are changed simultaneously, and a case in which a state of the first display layer and a state of the second display layer are changed separately; and a light outputting unit that irradiates light to the display medium.