A nonvolatile memory system includes a memory card (102) and host equipment (101). The memory card (102) includes a nonvolatile memory (106) including a plurality of physical blocks, and a memory controller (105) for writing data into the nonvolatile memory (106). The host equipment (101) provides to the memory card (102) an access instruction that designates a logical address and a channel number. The memory controller (105) has an address conversion function for converting the logical address into a physical address in the nonvolatile memory (106), a write destination determination function for determining in relation to the channel number a physical address in the nonvolatile memory (106) to which the data is to be written, and a channel management function for individually managing for each channel number a write state in which data of a smaller size than each physical block is written.