  We study the quotient of hypergeometric functions \begin{equation*}
\mu_{a}^*(r)=\frac{\pi}{2\sin{(\pi a)}}\frac{F(a,1-a;1;1-r^3)}{F(a,1-a;1;r^3)}
\quad (r\in(0,1)) \end{equation*} in the theory of Ramanujan's generalized
modular equation for $a\in(0,1/2]$, find an infinite product formula for
$\mu_{1/3}^*(r)$ by use of the properties of $\mu_{a}^*(r)$ and Ramanujan's
cubic transformation. Besides, a new cubic transformation formula of
hypergeometric function is given, which complements the Ramanujan's cubic
transformation.
