To provide an image generating method for improved noise characteristics by reducing noise, and for speeding up generation of an image.

The time series data related to pixel value measured and collected by a PET apparatus is developed in a feature space which is related to the waveform of time series data (step S1), which is projected onto two dimensional planes 1PC and 2PC for lower dimensions (step S2). The pixels in time series which show the same action on time base are classified into the same cluster, or clustering, (step S3), and then averaged for each cluster (step S4). Through these steps, noise is reduced for improved noise characteristics while generation of an image is speed up.