An air cleaning apparatus, especially for cleaning of room air, includes an ionizing device (14) having a unipolar ion source formed by a corona discharge electrode, an electrostatic precipitator (12) connected to a high-voltage source (15) and having a flow-through passageway (18) for air to be cleaned and two groups of electrode elements (16, 17) disposed in the flow-through passageway, the electrode elements (16) of one group being interleaved with and spaced from the electrode elements (17) of the other group and arranged to be at a potential different from that of the said other group. The corona discharge electrode (21) is arranged such that the ions generated at the electrode can diffuse essentially freely away from the electrode and thereby diffuse substantially freely throughout the room in which the ionizing device (14) is positioned.