Optical sheet forming device and optical sheet forming method

An optical sheet forming method comprising:

• spreading, by an extruding unit including an ejecting slit and configured to eject sheet-shaped molten resin, molten resin into a sheet shape;
• ejecting, by the extruding unit, the sheet-shaped molten resin;
• extruding, by the extruding unit, the ejected molten resin in the extrusion direction;
• solidifying and carrying, by a forming roll unit, the ejected molten resin from the extruding unit in the extrusion direction and
• forming, by a thick portion forming mechanism, one or a plurality of thick portions which are thicker than other portions in the sheet-shaped molten resin in a the process of extruding the molten resin continuously in the extrusion direction, wherein a thickness of a portion corresponding to the thick portion is greater than a thickness of the other portions in the ejected sheet-shaped ejected molten resin ejected, wherein:
• the ejecting slit comprises a standard gap portion where a gap having a constant size is formed in a direction crossing the extrusion direction, and
• the ejecting slit comprises an enlarged gap portion where a gap larger than the standard gap is formed in a position corresponding to the thick portion forming mechanism.