Flash memory device and reading method thereof

Provided are a flash memory device and a reading method of the flash memory device. A multi-level cell flash memory device includes: a memory cell array comprising main memory cells storing main data, and indicator cells storing indicate data indicating one of a first mode and a second mode in which the main data of the main memory cell, to which the indicate cells correspond, is written; and an output unit outputting in response to a control signal corresponding to the indicate data, one of main data read from the memory cell array and forced data forcing some bit values of the main data to bit values of mode specific data, as reading data.