To provide a pressure floatation type scum separation-processing apparatus, in which solubility of air can be made uniform by one having a structure which is simple and less in trouble.

In a pressure floatation type scum separation-processing apparatus configured to squirt collected scum-containing waste water into a floatation-separation tank 1 together with water that is generated by a pressure type air dissolution apparatus 70 which dissolves air by pressure, to float the scum in the same floatation-separation tank and at the same time to discharge the floated scum by a scum discharge apparatus, the pressure type air dissolution apparatus 70 includes: an air dissolution tank 71; and the air dissolution tank 71 is selected from a pressure tank type which dissolves air into separation-water by mixing the separation-water from the floatation-separation tank 1 with air from air supply means such as blower or compressor, and at the same time the air dissolution tank includes: internally a weight type flap valve 89 that opens by an internal pressure above a set level.