Provided are a processing block, a processing block holder, and a method of positioning a processing block with which, when a disk-shaped processing block is supplied to a processing device, axial centering of the processing block and the processing device can be easily achieved. A holding surface 1c comprising an inclined surface is formed extending from an upper edge of a flange 1b, which has a wider diameter than a portion 1a to be processed of a disk-shaped processing block 1, to the portion 1a to be processed, the holding surface 1c having the shape of the side surface of a cone. The processing block 1 is stored in an annular holding member 10 of a holding device and is moved forward with respect to a storage-side holding member 11 while being engaged with a pressing-side holding member 12, whereby a facing peripheral edge portion 12c of the pressing-side holding member 12 abuts against the holding surface 1c. Since the facing peripheral edge portion 12c abuts on a circle centered around the axis of the holding surface 1c of the cone, the axis of the annular holding member 10 and the axis of the processing block 1 are aligned with each other, and the processing block 1 is set at a predetermined location on the processing device.
