An adapter for a memory card is disclosed which performs a change of size so that a memory card smaller in planar size but almost equal in thickness as compared with a multi-media card can be used as a multi-media card. A protuberant portion is formed behind plural external terminals formed on a back side of the adapter, whereby, while the thickness of a front side of the adapter is maintained at a standardized thickness of the multi-media card, a rear side of the adapter is made thicker than the front side and internal terminals for contact with external terminals of the memory card are disposed in the interior of the thick portion of the adapter. The versatility of an extremely small-sized memory card can be improved.