A frame synchronizer, frame synchronization method and demodulator which can more positively establish frame synchronization of an input signal which is likely to have a plurality of frame lengths. A differential correlation detector calculates a differential correlation value with no pilot which is associated with the absence of a pilot signal inserted in the input signal and a differential correlation value with a pilot which is associated with the presence of a pilot signal inserted in the input signal. Frame period confirmation counters perform, based on the differential correlation values with no pilot, frame synchronization control appropriate to the input signals whose frame lengths are 21690 and 32490 symbols, respectively. The frame period confirmation counters 1 perform, based on the differential correlation values with a pilot, frame synchronization control appropriate to the input signals whose frame lengths are 22194 and 33282 symbols, respectively.