PURPOSE: To efficiently clean a press die with high safety and good accuracy by inserting the grinding tool having the grinding face of about the same dimension as that of a work relatively vibratably between the grinding face and forming face into the inner part of a closed die.

CONSTITUTION: A grinding tool 1 is inserted between an upper die 5a and lower die 5b by operating an arm 4b and subjected to a light rolling reduction with the upper and lower dies 5a, 5b by operating a hydraulic device 2. At this time, the grinding face 1a' of an upper grinding part 1a and the forming face 5a' of the upper die 5a come into collision, and the grinding face 1b' of a lower grinding part 1b and the forming face 5b' of the lower die 5b collide. In succession to the rolling reduction by this collision a fine vibration is generated by the vibration mechanism incorporated in the hydraulic device and a relative vibration is given between the grinding faces 1a', 1b' and forming faces 5a', 5b'. As a result, a closed die can uniformly grind to all the corners along its forming face, also the cleaning can be done safely with good efficiency in the state of the light contact of the grinding tool by utilizing the pressure of a press itself.