To clarify the role of the Golgi apparatus in photodynamic therapy–induced apoptosis, its signaling pathway was studied after photodynamic treatment of human cervix carcinoma cell line HeLa, in which a photosensitizer, 2,4,5,7-tetrabromorhodamine 123 bromide (TBR), was incorporated into the Golgi apparatus. Laser scanning microscopic analysis of TBR-loaded HeLa cells confirmed that TBR was exclusively located in the Golgi apparatus. HeLa cells incubated with TBR for 1 h were then exposed to visible light using an Xe lamp. Light of wavelength below 670 nm was eliminated with a filter. Morphological observation of nuclei stained with Hoechst 33342 revealed that apoptosis of cells was induced by exposure to light. Electron spin resonance spectrometry showed that light-exposed TBR produced both singlet oxygen (¹O₂) and superoxide anion (O₂^–). Apoptosis induction by TBR was inhibited by pyrrolidine dithiocarbamate, an O₂^– scavenger, but not by NaN₃, a quencher of ¹O₂. Furthermore, TBR-induced apoptosis was inhibited by aurintricarboxylic acid and ZnCl₂, which are known as inhibitors of deoxyribonuclease (DNase) γ, and (acetoxymethyl)-1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid, a chelator of Ca² , but not by acetyl Asp-Glu-Val-Asp-aldehyde, an inhibitor of caspase-3. These results suggested that O₂^– was responsible for TBR-induced apoptosis, and Ca² -dependent and caspase-3–independent nuclease such as DNase γ played an important role in apoptotic signaling triggered by Golgi dysfunction.