To provide mounting system of disc-shaped tool allowing easy discharge of interfering particles and dust.

In this system provided with a tool holding part 10, the tool holding part 10 includes an association device 12, and a disc-shaped insertable tool 14 can be effectively coupled to a drive shaft 16 via the association device. At least one of first function elements 18, 20 has at least one of holding regions 22, 24 and 26. At relative motion between the first function elements 18, 20 and second function elements 14, 28, 30, the interfering particle is held inside the holding regions.