A frame sync detecting circuit for detecting frame synchronization from a received word pattern, the frame sync detecting circuit comprising: an average-value calculation section operable to calculate a moving average value of a given number of moving values of the received word pattern; said frame sync detecting circuit being characterized in that it further comprises: an offset calculation section operable, using a moving average value of moving values of a same number as the given number, in a predetermined sync word pattern, as an ideal average value, to calculate a DC offset from a difference between the ideal average value and the moving average value calculated by the average-value calculation section; a subtraction section operable to subtract the DC offset from respective symbol values of the received word pattern; a correlation processing section operable to perform a correlation processing between the received word pattern after the DC offset subtraction by the subtraction section, and the predetermined sync word pattern; a candidate determination section operable to compare a correlation value derived by the correlation processing section with a predetermined threshold value, wherein the candidate determination section is operable, if the correlation value is greater than the threshold value, to recognize the received word pattern as a sync word candidate; and a final determination section operable, when a sync word candidate is recognized by the candidate determination section, to compare symbol values of the received word pattern after the DC offset subtraction with corresponding symbol values of the predetermined sync word pattern, wherein the final determination section is operable, if sum of differences of all the symbol values fall within a given range, to determine that a sync word pattern is detected. an average-value calculation section operable to calculate a moving average value of a given number of moving values of the received word pattern; said frame sync detecting circuit being characterized in that it further comprises: an offset calculation section operable, using a moving average value of moving values of a same number as the given number, in a predetermined sync word pattern, as an ideal average value, to calculate a DC offset from a difference between the ideal average value and the moving average value calculated by the average-value calculation section; a subtraction section operable to subtract the DC offset from respective symbol values of the received word pattern; a correlation processing section operable to perform a correlation processing between the received word pattern after the DC offset subtraction by the subtraction section, and the predetermined sync word pattern; a candidate determination section operable to compare a correlation value derived by the correlation processing section with a predetermined threshold value, wherein the candidate determination section is operable, if the correlation value is greater than the threshold value, to recognize the received word pattern as a sync word candidate; and a final determination section operable, when a sync word candidate is recognized by the candidate determination section, to compare symbol values of the received word pattern after the DC offset subtraction with corresponding symbol values of the predetermined sync word pattern, wherein the final determination section is operable, if sum of differences of all the symbol values fall within a given range, to determine that a sync word pattern is detected. an offset calculation section operable, using a moving average value of moving values of a same number as the given number, in a predetermined sync word pattern, as an ideal average value, to calculate a DC offset from a difference between the ideal average value and the moving average value calculated by the average-value calculation section; a subtraction section operable to subtract the DC offset from respective symbol values of the received word pattern; a correlation processing section operable to perform a correlation processing between the received word pattern after the DC offset subtraction by the subtraction section, and the predetermined sync word pattern; a candidate determination section operable to compare a correlation value derived by the correlation processing section with a predetermined threshold value, wherein the candidate determination section is operable, if the correlation value is greater than the threshold value, to recognize the received word pattern as a sync word candidate; and a final determination section operable, when a sync word candidate is recognized by the candidate determination section, to compare symbol values of the received word pattern after the DC offset subtraction with corresponding symbol values of the predetermined sync word pattern,