A data receiver which enhances a probability of frame synchronization even if a transmission line quality is bad detects a specific bit sequence in a received signal demodulated by a demodulator to deduce a transmission line quality by a line quality deducer. If the transmission line quality is so bad that a frame synchronization detector cannot detect the specific bit sequence, the specific bit sequence is detected from a received signal demodulated by an equalizer after the elimination of a transmission line distortion.
