Nonvolatile memory

There is provided a technology to realize high speed data transfer while compatibility of a card type storage device comprising a nonvolatile memory is ensured. Namely, in the card type storage device comprising the nonvolatile memory, a plurality of data terminals are provided and an interface unit is provided with a circuit for determining levels of data terminals. Some or all of the plurality of data terminals are connected with pull-up resistors for pulling up to a power source voltage. When the determination circuit determines that the data terminals connected with the pull-up resistors are in an open condition, the determination circuit switches a bus width (number of bits) of data.