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.