A phase locking apparatus is disclosed which, includes a phase error
information detecting device to detect phase error information indicating
the phase error. The device has a phase position determining device to
determine, based on run length limited information, whether or not phase
positions of a first and second value from among sampling values
constituting synchronous data are under a reverse phase condition in
effect when only one of the first and the second values is in excess of a
predetermined threshold, and a phase error information calculating device
to calculate the phase error information in each of two cases determined,
one with the reverse phase condition found to be in effect and the other
without effect.