Non-uniform pressure distribution on shrouded co-rotating disks at high speed causes disk flutter. For stable rotation of disks at high speed, it is necessary to analyze pressure distribution on the disk surfaces and understand the mechanism of the disk flutter. To clarify the behavior of the flow around high-speed co-rotating disks, we have measured pressure distribution of disk surfaces by means of pressure sensitive paint. As a result, it is clarified that the pressure difference between the outer part and the inner part of the middle disk of the triple co-rotating disks is larger than that of the top disk, and the average pressure on the middle disk is lower than that of the top disk.