  We investigated the temporally evolving network structures of the Japanese
and Korean stock markets through the minimum spanning trees composed of listed
stocks. We tested the validity of conventional grouping by industrial
categories, and found a common trend of decrease for Japan and Korea. This
phenomenon supports the increasing external effects on the markets due to the
globalization of both countries. At last the Korean market are grouped with the
MSCI Korea Index, a good reference for foreigners' trading, in the early 2000s
\cite{Jung2006}. In the Japanese market, this tendency is strengthened more and
more by burst of the bubble in 1990's.
