Dentsu Inc . , founded in 1901 , is the largest advertising company brand and the fifth largest marketing and communications organization in the world . Based in Tokyo , the group has more than 6,000 clients and more than 17,503 full-time employees * in both Japan and in its offices overseas . Consolidated billings ( net sales ) for fiscal year 2007 were recorded at $ 20,536 million . Dentsu is publicly quoted on the Tokyo Stock Exchange ( Code 4324 ) .