\documentclass{jarticle}
\usepackage{multirow}
\usepackage{array}
\newcolumntype{Y}{>{\centering\arraybackslash}p{4zw}} 
\begin{document}
\begin{table}[htbp]
\caption{キャプション}
\centering
{\small
\begin{tabular}{|Y|Y|Y|p{3ex}|Y|Y|Y|} \cline{1-3}\cline{5-7}
\multicolumn{3}{|c|}{a}&&\multicolumn{3}{c|}{a}\\ \cline{1-3}\cline{5-7}
a&a&a& &a&a&a\\ \cline{1-3}\cline{5-7}
\multirow{2}{4zw}{\hfill a\hfill }&a&a& &\multirow{2}{4zw}{\hfill a\hfill}&a&a\\
                                 &a&a& & &a&a\\ \cline{1-3}\cline{5-7}
\multirow{2}{4zw}{\hfill a\hfill }&a&a& &\multirow{2}{4zw}{\hfill a\hfill}&a&a\\
                                 &a&a& & &a&a\\ \cline{1-3}\cline{5-7}
\multirow{2}{4zw}{\hfill a\hfill }&a&a& &\multirow{2}{4zw}{\hfill a\hfill}&a&a\\
                                 &a&a& & &a&a\\
\cline{1-3}\cline{5-7}
\end{tabular}}
\end{table}
\end{document}
