A mechanism for chucking a disk with a first and a second roller includes a base plate provided substantially at a right angle to a surface of the disk, and a first and a second rod that are spaced apart and which move along the base plate either toward or away from the disk. A first block is provided which, when the first rod advances or retracts, moves along the base plate and substantially parallel to the surface of the disk, and a first roller is mounted on the first block. A second block is provided which, when the second rod advances or retracts, moves either toward or away from the first roller and the disk, and a second roller is mounted on the second block. A roller position setting mechanism which is secured to the base plate is provided which allows the first rod to move either toward or away from the disk, thereby causing the first block to move along the base plate such that the first roller comes to a position associated with the size of the disk. A drive mechanism is provided for allowing the first and second rods to move either toward or away from the disk.