Dentsu who is the biggest advertising company in Japan has released a report of Advertising cost in Japan in 2013. Here is the data (All in Japanese). 2013年 日本の広告費は5兆9762億円(PDF)

They mention about Internet advertising spend as below.

Internet Ads spending
– Internet Ads spending (Including Media and fabrication cost) 938.1 billion (YoY 108.1%)
– Big growth in 2013 because of various devices and better economy than in 2012. Search Engine Ads showed a high growth.

– Due to smarphones and tablets, Search Engine Ads have been expanding continuously. Also new technologies like RTB and DSP has become popular advertising ways. Finance and Insurance have kept spending money for the Search Ads. In addtion to that, other industries like Car, Foods, Beverages and Articles have started using the Search Ads for their branding.

Ads expenses Japan 2013
Reference: http://www.dentsu.co.jp/news/release/2014/pdf/2014014-0220.pdf

The SEM market has still expanding since 2003. Those companies spend their money for SEM because they find an efficiency on the ads as the number ‘938.1 billion’ shows.