A TWA measuring apparatus includes: a T-wave feature quantity measuring section; a classifying section classifying T-wave feature quantities into groups of odd and even electrocardiogram waveforms; a reliability index calculating section calculating: first and second representative values and first and second dispersion values of the T-wave feature quantities in the odd and even group; a difference between the first and second representative values, to obtain a TWA feature quantity; and an adjustment value between the first representative value and the first dispersion value, and an adjustment value between the second representative value and the second dispersion value, to obtain a reliability index; and a reliability recognizing section recognizing: when the reliability index exceeds a threshold, that reliability of the TWA feature quantity is high; and when the reliability index does not exceed the threshold, that the reliability is low.