  An action of ${\mathbb Z}^k$ is associated to a higher rank graph $\Lambda$
satisfying a mild assumption. This generalises the construction of a
topological Markov shift arising from a nonnegative integer matrix. We show
that the stable Ruelle algebra of $\Lambda$ is strongly Morita equivalent to
$C^*(\Lambda)$. Hence, if $\Lambda$ satisfies the aperiodicity condition, the
stable Ruelle algebra is simple, stable and purely infinite.
