An improved skin substitute is presented comprised of non-biological materials produced with a series of regularly-spaced pores and a nylon weave netting. The control unit detects a deterioration state of the polarization control element based on the projected image which is taken by an image-taking unit when a test image representing a single color throughout a screen is projected. The feedback circuit includes a first diode connected to a first sensing voltage corresponding to output voltage and a second diode connected to the output voltage. Further an internal clock generating circuit is formed in the panel and supplies the first clock signal HCK to the horizontal driving circuit in accordance with the second clock signal DCK.