Bidirectional transmission of write and read data is effected between a reader/writer unit and a memory module in a contactless manner using electromagnetic induction coupling. A single magnetic induction coupling apparatus is provided for each of the reader/writer unit and the memory module. In the electromagnetic induction coupling apparatus of the reader/writer unit, a transmitting coil and a receiving coil are coaxially wound around a single magnetic core. In the electromagnetic induction coupling apparatus of the memory module, a single coil which is commonly used for transmission and reception is wound around a single magnetic core. A reception signal of the transmitting/receiving coil of the memory module is rectified and smoothed by a power source circuit, thereby forming an operating power source of the memory module. The power source circuit has a backup capacitor. In the transmitting mode in which no power source is externally supplied, the operating power source is supplied from the backup capacitor.