Abstract: A digital multi-frequency receiver for the use in an electronic telephone exchange system for detecting MF signals (700,900, 1100, 1300, 1500 and 1700 Hz) in the CCITT No. 5 system. The digital multi-frequency receiver comprises a recursive digital filter for detecting each of the MF signals on a time divisional basis, an absolute value circuit for providing the absolute value of the output of the recursive digital filter, a comparator for comparing the output of the absolute value circuit with a variable threshold to provide the detected MF signal information, and a circuit for providing the variable threshold by selecting the maximum value from among, (i) the predetermined fixed value, (ii) the product of the value .alpha. which is less than but close to 1 and the maximum value of the variable threshold circuit in a preceding frame, and (iii) the maximum value of the output of the absolute value circuit in a present frame.