PURPOSE: An optical characteristic improvement method through an application of waste paper and a synthesis of precipitated calcium carbonate using rough limestone is provided to increase the whiteness of recycled paper and lower the concentration of the extant ink by performing synthesis of in-situ and waste paper pulp by plasticizing rough limestone. CONSTITUTION: An optical characteristic improvement method through an application of waste paper and a synthesis of precipitated calcium carbonate using rough limestone comprises: a rough limestone plasticizing step(1), a recycled paper preparing step(2), a CO2 spraying step(3), a carbonation reaction step(4), a slurry recovering step(5), and a recycled paper manufacturing step(6). The rough limestone is plasticized at 100 deg C. After the rough limestone is plasticized, CaO component is produced. Through the carbonation reaction of the CaO component, PCC is synthesized on the waste paper pulp by in-situ method. The recycled paper manufactured through the optical characteristic improvement method has the extant ink concentration of 30ppm and 85% or more of whiteness. [Reference numerals] (1) Plasticizing rough limestone; (2) Preparing recycled pulp(ONP, OMG); (3) Spraying carbon dioxide; (4) Carbonation; (5) Collecting slurry; (6) Manufacturing recycled paper; (7) Analysis