A floating-disk type brake system that includes floating disk assemblies placed respectively in spaces between a rotating member, such as a wheel of a transportation machine or a rotating shaft of a machine tool, and a stationary member to reduce differences in the rotating speed of adjacent sliding surfaces of the floating disk assemblies in frictional sliding engagement. The floating-disk type brake system includes a first floating disk assembly and a first disk assembly that are arranged between the ring gear and the planet carrier of a planetary gear built in a transmission or the like, and the first floating disk assembly and the first disk assembly are pressed together into frictional engagement to brake a rotating shaft.