An ozone generating apparatus which comprises a plurality of chambers filled with an adsorbent, wherein a wet raw air is fed through one of the chambers filled with the adsorbent to adsorb moisture to form a dry air and the dry air is fed into an ozonizer to convert it into a dry ozone-containing air, and all or part of the dry ozone-containing air is fed into the other chamber filled with the adsorbent to purge water adsorbed on the adsorbent and to discharge it as a wet ozone containing air. The valves are then switched to feed the wet air to the other chamber filled with the adsorbent, whereby the moisture is adsorbed and the dry ozone-containing air fed from the ozonizer is fed into the former chamber filled with the adsorbent to reactivate the adsorbent and to discharge it as the wet ozone-containing air. The cycle is continuously repeated by switching valves.