PURPOSE: A dual-tone detecting device is provided to greatly reduce talk-down and talk-off error by deciding whether or not the signal size of respective tone is greater than prescribed value and the difference between tones is less than prescribed value and deciding whether or not the positive band composite of respective tone is greater than peripheral frequency. CONSTITUTION: The dual-tone detecting device comprises: a upper tone positive band-pass filter(430) for upper tone; a upper tone upper band-pass filter(420) for upper tone; a upper tone lower band-pass filter(440) for upper tone; a upper tone positive-upper band comparator(450); a upper tone positive-lower band comparator(460); a lower tone positive band-pass filter for lower tone; a lower tone upper band-pass filter for lower tone; a lower tone lower band-pass filter for lower tone; a lower tone positive-upper band comparator; a lower tone positive-lower band comparator; and a dual-tone detecting decision unit.
