Business confidence of large Japanese manufacturers improved in the fourth quarter of 2013, with the index reaching the highest level in six years, local media reported Monday. According to the Tankan report released by the Bank of Japan, sentiment among big manufacturers such as carmakers and high-tech firms rose to plus 16 from September's plus 12, supported by improvement in corporate earnings amid a weakening yen. The quarterly survey said sentiment among nonmanufacturing companies such as those related to construction and services gained 6 points to plus 20 from the previous quarter, higher than the average estimate of plus 16. The index for small manufacturers climbed 10 points to plus 1 and that for small nonmanufacturers rose 5 points to plus 4, the first time in about 22 years for the latter entering positive territory. The survey was conducted between Nov. 14 and Dec. 13 on 10,509 companies, of which 99.4 percent responded. The diffusion index represents the percentage of companies reporting favorable business conditions minus that of firms describing unfavorable environments.