\documentclass{jarticle}
\usepackage{amsmath}
\usepackage{multirow}

\begin{document}

\begin{center}
\begin{tabular}{|c|c|c|c|c|c|}
\hline
\multirow{2}{3zw}{\hfill$r$\hfill} & 観測度数 & 確　率 & 期待度数    & \multirow{2}{7zw}{\hfill$(x_r-np_{r0})^2$\hfill} & \multirow{2}{7zw}{\hfill$\dfrac {(x_r-np_{r0})^2}{np_{r0}}$\hfill} \\[-5pt]
                       & $x_r$    & $p_{r0}$ & $np_{r0}$ &                                      &                                                         \\[4pt]
\hline
0 & 170 & 0.445 & 162.4 & 57.76 & 0.356\\
\hline
1 & 125 & 0.360 & 131.4 & 40.93 & 0.312\\
\hline
2 & 50 & 0.146 & 53.3 & 10.89 & 0.204\\
\hline
3 & 13 & 0.039 & 14.2 & 1.44 & 0.101\\
\hline
4 & 7 & 0.010 & 3.7 & 10.89 & 2.943\\
\hline
\end{tabular}
\end{center}

\end{document}
