An apparatus for measuring a periodic physical information of a living subject, including a measuring device which iteratively measures, from the subject, a value of the periodic physical information including a periodically changing component, a waveform determining device for determining a changing-component waveform representing the periodically changing component of the periodic physical information, a difference determining device for determining at least one difference between at least one first value of the periodic physical information measured by the measuring device at at least one time and at least one second value of the changing-component waveform at the at least one time, and a removing device for judging, based on the at least one difference determined by the difference determining device, whether the at least one first value is abnormal, and removing the at least one first value judged as being abnormal.