In a reconstruction processing (S1), reconstruction processing is performed to list mode data to firstly capture a reconstruction image. Then, in a projection step (S2), the reconstruction image obtained in the reconstruction processing step is projected to capture a projection image. In a scatter component extracting step S4, low-frequency components are extracted from the projection image obtained in the projection step to obtain scatter components. Even when the data contains a missing region, the reconstruction processing unlikely to be influenced by the missing region suppresses the influence by the missing, and the resultant reconstruction image is projected. Consequently, the projection image having dummy data being interpolated to the missing region is obtainable. As a result, projection from the list mode data through the reconstruction image achieves the projection image with no missing data. Accordingly, precious estimation of the scatter components is obtainable.