We developed a DICOM interface for Geant4-based medical physics applications. Geant4 simulation toolkit has been adopted to radiotherapy, hadrontherapy, PEM, PET, MRT and so on, in purpose of physical full-simulation of accurate particle propagation and interaction with not only medical devices but also patient tissues. DICOM is commonly utilized to transport digital images such as patient image, information and so on. We succeeded in retrieving various manufacturers' DICOM data stream, constructing Geant4 geometry and simulating particle interaction with patient tissues in a Geant4 application with the DICOM interface. In addition, the DICOM interface can store outcomes of the simulation successively as a DICOM data stream; consequently commercially or freely available DICOM viewers come to be usable to visualize results. In this paper, we describe feature and availability of the DICOM interface.