1. An X-ray CT (Computed Tomography) device comprising: a data collection section including at least an X-ray tube and an X-ray detector for imaging a subject with N different types of energy distributions so as to obtain N types of projection data; and a processor programmed to: convert the obtained N types of projection data into N+1 types of reference substance penetration distance data for N+1 types of reference substances which are reconstructed to obtain reference substance equivalent tomographic images, wherein the processor is further programmed to obtain the reference substance penetration distance data of a first substance contained in the N+1 types of reference substances by executing a p-value conversion of a first image reconstructed using the N types of projection data for reprojection, determining a contribution of the first substance in the N types of projection data using the obtained reference substance penetration distance data for removing the contribution, and converting the projection data after removing the contribution into the reference substance penetration distance data for image reconstruction so as to obtain N+1 types of reference substance equivalent tomographic images, and wherein the processor is further programmed to execute q-value conversion of one of the reference substance equivalent tomographic images with respect to a second substance contained in the N+1 types of reference substances, which is different from the first substance, and to determine contributions of the first and second substances in the N types of projection data using the reprojected reference substance penetration distance data so as to obtain the N+1 types of reference substance equivalent tomographic images which are different from the reference substance equivalent tomographic images of the first and second substances.