The present invention is intended to provide an economical printer which is simple in structure and uses a common tray but is capable of adapting itself to various recording media of different shapes. Adapters in which recording media can be fitly held can be selectively mounted in the tray. An adapter (24) has an oval opening (24a) in which a recording medium (30) can be fitted. The contour of the adapter (24) can fit into a recessed portion (23a) formed in the tray (23). The recording medium (30) is fitly held in the adapter (24). When the adapter (24) is mounted in the recessed portion (23a) in the tray (23), a keyway (23b) and a protrusion (24b) engaging the keyway (23b) prevent the adapter (24) from shifting out of position; the adapter is held in the tray (23). Prints can be made in accurate positions on the recording medium (30).