In 1994, carbon ion radiotherapy was begun at the NIRS (National Institute of Radiological Sciences) using HIMAC (Heavy-Ion Medical Accelerator in Chiba), which was the world's first heavy ion accelerator complex dedicated to medical use in a hospital environment. Among several types of ion species, carbon ions were selected for cancer therapy because they presumably had the most optimal properties in terms of biologically effective dose-localization. The purpose of the clinical study of carbon ion radiotherapy was to investigate the efficacy of carbon ions against a variety of tumors as well as to develop effective and safe techniques for delivering the efficient dose to the tumor. As of February 2013, a total of 7,339 patients were treated with carbon ion radiotherapy. The results have shown that carbon ion radiotherapy has the ability to provide a sufficient dose to the tumor without unacceptable morbidity in the surrounding normal tissues. Tumors that appear to respond favorably to carbon ions include locally advanced tumors and those with histologically non-squamous cell type of tumors such as adenocarcinoma, adenoid cystic carcinoma, malignant melanoma, hepatoma, and bone and soft tissue sarcomas. By using biological and physical properties of the high-LET carbon ion beams, the efficacy of treatment regimen with small fractions in shorter treatment course has been confirmed for almost all type of tumors in our carbon ion radiotherapy experience. Based on these experiences, we embarked on the research and development of a new generation beam delivery facilities such as a 3D-scanning method with a pencil beam and a compact rotating gantry. A clinical research using the pencil beam scanning was in operation since May 2011. The 3rd Asian Congress of Radiation Research