There is provided a biological signal processing apparatus. The biological signal processing apparatus includes a biological signal extraction unit (2) configured to extract a biological signal from an electrocardiographic waveform measured by an electrocardiograph (1), an averaging processing unit (3) configured to calculate averaged data using time-series data of the biological signals extracted by the biological signal extraction unit (2), an abnormal value determination unit (4) configured to determine, for each data, whether the data of the biological signal extracted by the biological signal extraction unit (2) is appropriate, based on the averaged data calculated using the data of the biological signals that have occurred before the data, and an abnormal value processing unit (5) configured to perform one of deletion and interpolation of the data of the biological signal determined to be inappropriate by the abnormal value determination unit (4).