Flash memory device storing data with multi-bit and single-bit form and program method thereof

A flash memory device storing data into a multi bit mode and a single bit mode, and a program method thereof are provided to prevent programming or removing of a division information block in programming or removing a memory cell array. A memory cell array(210) includes a plurality of memory blocks and a division information block. Division information indicates a boundary of the memory blocks set into a multi bit mode and a single bit mode among the memory blocks, and is stored in the division information block. A control logic(250) determines the multi bit mode or the single bit mode of the memory block based on the division information, and controls a programming and reading operation into the multi bit mode or the single bit mode based on a determined result. A fuse(253) is connected to the control logic.