  For a real number $0<\lambda<2$, we introduce a transformation $T_\lambda$
naturally associated to expansion in $\lambda$-continued fraction, for which we
also give a geometrical interpretation. The symbolic coding of the orbits of
$T_\lambda$ provides an algorithm to expand any positive real number in
$\lambda$-continued fraction. We prove the conjugacy between $T_\lambda$ and
some $\beta$-shift, $\beta>1$. Some properties of the map
$\lambda\mapsto\beta(\lambda)$ are established: It is increasing and continuous
from $]0, 2[$ onto $]1,\infty[$ but non-analytic.
