The electric current flow upon illumination of the TiO2electrode in ann‐TiO2/KOH/Pt photolytic cell without auxiliary external voltage is related to the production of hydrogen or the reaction with dissolved oxygen at the Pt electrode depending on the electrolyte and the atmosphere above the electrolyte. Since hydrogen is produced with a pressure of much less than atmospheric pressure, no bubbles appear at the Pt electrode. The pressure and the production rate of the generated hydrogen are determined by the depth of immersion of the Pt electrode. The increase of both pressure and production rate of hydrogen upon application of an auxiliary voltage, as well as the energy‐level diagram of the photolytic cell, are discussed on the basis of the experiments carried out without auxiliary voltage.