Multiple myeloma is a kind of malignant disease in the organ which produce blood cells such as bone marrow. It has poor prognosis, especially in patients who are relapsed repeatedly. Effective treatment is strongly expected in such relapsed patients in Japan. This is a open label multiple center study to evaluate the effectiveness and safety of bortezomib. This study is an extension or re-treatment study for patients who were administered with bortezomib in preceding Phase I/II study. For extension treatment, the same dose of the previous study will be administered into a vein as a bolus twice weekly followed by a 10-day rest (3-week cycle). For re-treatment, a recommended dose determined in Phase I/II study will be administered in 3-week cycle.