It is an object to provide a partition plate device capable of rendering a light guide plate function as a transparent member likewise a window plate and as a light shielding member used as an area light source having a prescribed pattern. The invented partition plate device includes a light guide plate having, on double sides as major surfaces thereof, plural recess pattern scars formed partly melting through vibration of ultrasound under contacting fabrication dots provided in a matrix shape at an ultrasound fabrication horn to major surfaces thereof with pressure; and a light source unit rendering light enter from a side surface of the light guide plate and diffused light occur from the recess pattern scars, wherein the light guide plate functions as a transparent member while no light enters from the light source unit and functions as a light shielding member made of an area light source having a prescribed pattern formed with the recess pattern scars while light enters from the light source unit.