Abstract: A disk adapter A is equipped with first and second adapter halves 1 and 2 to be detachably disposed in a disk-placing dented portion 54 provided in a disk tray 53 of a label printer 51. One of the adapter halves 1 and 2 is movable relative to the other thereof in accordance with a movement of a disk pushing member 55 provided in the disk tray 53. When the disk tray 53 is inserted into a printer main body 52, the aforementioned one of the adapter halves is moved in a direction that the one of the adapter halves approaches the other thereof by the disk pushing member 55, whereby the optical disk D is held by and between both the adapter halves 1 and 2.