An upsampler 22 performs upsampling based on actual measurement data forming a profile spectrum obtained with a time-of-flight mass spectrometer 1, to insert interpolation data between the temporally adjacent actual measurement data and make the waveform smoother. Subsequently, a peak waveform processor 23 determines the centroid position, peak area or other relevant values by performing centroid processing which employs trapezoidal approximation or similar technique. The smoothing of the waveform between adjacent measurement data improves the accuracy of the centroid processing, whereby a systematic error in the estimation of the centroid position or calculation of the peak area is reduced. Therefore, even when the number of data points forming one peak on a measured waveform is small, the centroid position and other kinds of peak information can be obtained with a high level of accuracy, and the performance of qualitative or quantitative determination is thereby improved.