A machine tool includes a main shaft unit; a polishing head for processing a workpiece; and an unnecessary byproduct leakage preventing unit for preventing leakage of abrasive resulting from processing at or around a part of the workpiece, the part being processed, and wherein the unnecessary byproduct leakage preventing unit includes a cover provided separately from the polishing head, the cover having a structure that is open in three directions and that has walls in another three directions such that a protection space where to hold a part of the workpiece is defined, the cover for receiving the abrasive, and a movement mechanism for moving the cover so as to stay apart from the workpiece while the workpiece is not being processed and so as to have a part of the workpiece held in the protection space while the workpiece is being processed.