A blood pressure data processing apparatus including a peak selection unit, a frequency component suppression unit, a respiratory fluctuation calculation unit, an attenuation amount calculation unit, and a respiratory cycle determination unit. The frequency component suppression unit suppresses components of the selected peak frequency within the first spectrum, and generates a second spectrum. The respiratory fluctuation calculation unit calculates a first respiratory fluctuation in second blood pressure data, and calculates a second respiratory fluctuation in third blood pressure data, which is a time domain representation of the second spectrum. The attenuation amount calculation unit calculates an attenuation amount of the second respiratory fluctuation relative to the first respiratory fluctuation. The respiratory cycle determination unit determines a cycle corresponding to the selected peak frequency as a respiratory cycle of a user if the attenuation amount is greater than a threshold.
