  The thermodynamic formalism for dynamical systems with many degrees of
freedom is extended to deal with time averages and fluctuations of some
macroscopic quantity along typical orbits, and applied to coupled map lattices
exhibiting phase transitions. Thereby, it turns out that a seed of phase
transition is embedded as an anomalous distribution of unstable periodic
orbits, which appears as a so-called q-phase transition in the spatio-temporal
configuration space. This intimate relation between phase transitions and
q-phase transitions leads to one natural way of defining transitions and their
order in extended chaotic systems. Furthermore, a basis is obtained on which we
can treat locally introduced control parameters as macroscopic ``temperature''
in some cases involved with phase transitions.
