\def\use@mathgroup#1#2{\relax\ifmmode
\math@bgroup
\expandafter\ifx\csname M@\f@encoding\endcsname#1\else
- #1\fi\ltj@tempcnta=#2 \expandafter\ltj@@mathJapaneseFonts\string#1\relax%
+ #1\fi\ltj@tempcnta=#2
+ \expandafter\ltj@@mathJapaneseFonts\string#1/\relax%
\ifin@\jfam#2\relax\else\mathgroup#2\relax\fi
\expandafter\math@egroup\fi}%