1. A nonvolatile memory controller for controlling a nonvolatile memory configured from a plurality of physical blocks, comprising: a control unit for controlling writing and/or reading of data to and from the physical block based on a logical address, from an external device, within an effective logical address range from a minimum logical address to a maximum logical address; a logical defective cluster table for storing information concerning a logical address of a logical defective cluster which is one or more partial areas within the effective logical address range and in which reflection of the writing of data to the logical address is disabled; and an address conversion table for storing corresponding information of a logical address of the effective logical address range and a physical address of the physical block on the data stored in the physical block, wherein, upon receiving a data write command from the external device for writing data to the logical address stored in the logical defective cluster table, the control unit disables the reflection of writing of data for the logical address to the physical block.