\documentstyle[a4j]{j-article} \begin{document} % \begin{equation} \label{kakezan} \left( \begin{array}{c} b_{1} \\ b_{2} \\ b_{3} \end{array} \right) = \left[ \begin{array}{ccc} a_{11} & a_{12} & a_{13} \\ a_{21} & a_{22} & a_{23} \\ a_{31} & a_{32} & a_{33} \end{array} \right] % \left( \begin{array}{c} x_{1} \\ x_{2} \\ x_{3} \end{array} \right) \end{equation} % \end{document} %