This paper reports a novel approach for the simple detection of cell apoptosis using an electrochemical technique. This method uses caspase-3 activity as an indicator of apoptosis. Caspase-3 activity was detected with differential plus voltammetry (DPV) as an alternative to conventional spectrometry. In this method, p-nitroaniline (pNA) released from Asp-Glu-Val-Asp-pNA by caspase-3 enzyme reaction was measured with DPV by using a glassy carbon electrode. Using this method, we successfully detected cell apoptosis occurring inside living HepG2 cells without the need for a cell lysis step. This method provides an easy assay procedure and, more importantly, allows a live cell apoptosis detection format. This novel electrochemical apoptosis assay using living cells instead of typically used cell lysates will expand the applicable range of the apoptosis assay to include cell activity assays for drug discovery and cell transplantation medicine.