\documentclass[12pt]{jsarticle}
\usepackage{amsmath,amsthm,txfonts}

\makeatletter

%----- Equation num brackets -------------------

\newcommand\eqnobrck[1]{[#1]}

%---- Test if a file is loaded ------------------

\newcommand\@iffileloaded[2]{%
    \expandafter\ifx\csname ver@#1.#2\endcsname\relax
       \expandafter\@secondoftwo
    \else
       \expandafter\@firstoftwo
    \fi}

%----- For right equation numbers --------------

\renewcommand\@eqnnum{{%
    \normalfont \normalcolor \eqnobrck{\theequation}}}

%---- For left equation numbers ----------------

\@iffileloaded{leqno}{clo}{%
    \renewcommand\@eqnnum{\hb@xt@.01\p@{}%
       \rlap{\normalfont\normalcolor
       \hskip -\displaywidth\eqnobrck{\theequation}}}
    }{}

%---- If amsmath is loaded ----------------------

\@ifpackageloaded{amsmath}{%
     \renewcommand\tagform@[1]{%
        \maketag@@@{\eqnobrck{\ignorespaces#1\unskip\@@italiccorr}}}
        }{}


 \renewcommand{\theequation}{%
   \thesection.\arabic{equation}}
  \@addtoreset{equation}{section}


\makeatother

\begin{document}

\section{�͂���}

\begin{equation}
f(x)=x^3
\end{equation}

\begin{align}
g(x)&=x+8\\
&=8+x
\end{align}

\end{document}
