\documentclass{jarticle}

\newcommand{\keybox}[1]{%
   {%
     \setlength{\fboxsep}{.2ex}%
     \setlength{\fboxrule}{.07em}%
     \framebox{\textsc{#1}\vphantom{無変換}}% 漢字の高さ
   }%
}

\begin{document}

\keybox{Alt}
\keybox{F1}
\keybox{Delete}
\keybox{無変換}

\end{document}
