A dissolved air floatation apparatus including an ultrafine bubble-containing liquid production device and a dissolved air floatation tank. The ultrafine bubble-containing liquid production device includes a gas-liquid mixing unit and a bubble-containing liquid separation device. The bubble-containing liquid separation device swirls a liquid containing ultrafine bubbles and larger bubbles in a storage tank to concentrate the liquid that contains the ultrafine bubbles and the liquid that contains the larger bubbles to a central part of the swirling flow followed by discharge. A pressurized ultrafine bubble-containing liquid is mixed in a raw liquid containing a subject to be cleansed and is poured into the dissolved air floatation tank to cause a suspended substance and a dissolved component in the raw liquid to be adsorbed on an interface of fine bubbles and be floated in the dissolved air floatation tank to be extracted.