A refiner is formed of a plurality of first disc members provided on a casing and divided along a circumferential direction thereof; a plurality of first connecting members for fixing the first disc members to the casing; a plurality of second disc members provided on a runner with a rotating shaft, the second disc members facing the first disc members and divided along a circumferential direction thereof; and a plurality of second connecting members for fixing the second disc members to the runner. The refiner also includes engaging members provided on outer peripheral surfaces except for blade faces of the first disc members or the second disc members; and engaged members provided on at least one of the casing or the runner. When the rotating shaft is rotated, loads applied to the first connecting members or the second connecting members can be reduced greatly.