The purpose of this study is to assess the efficacy and safety of SyB L-0501 (two-day consecutive 90 mg/m2/day IV drip infusions) in combination with rituximab (375 mg/m2 IV drip infusion) on untreated, low-grade B cell non-Hodgkin's lymphoma and mantle cell lymphoma where hematopoietic stem cell transplantation is not indicated.