A flash memory device may include a memory cell array including a plurality of memory blocks and a partition information block, the partition information block storing partition information that indicates a boundary between multi-bit memory blocks and single-bit memory blocks among the memory blocks. The memory device may include a control logic configured to determining whether a memory block that a block address from the outside indicates has a multi-bit form or a single-bit form based on the partition information and to control program and read operations in a multi-bit form or a single-bit form based on a determination result. The control logic automatically programs data in the partition information block according to whether a fuse connected to the control logic fuse is cut or not, the data being used for preventing the partition information block from being programmed or erased.