1. A method for managing a bad block in a flash memory, comprising: (a) allocating a used area comprising a plurality of used blocks and a spare area comprising a plurality of spare blocks in the flash memory, and providing a block map page group including a plurality of block map pages in which mapping information to map a bad block generated in either the used area or the spare area to a first spare block is disposed; (b) having the mapping information of the block map page selected by a predetermined rule, which belongs to a block map page group, reside in a main memory as resident mapping information; and (c) mapping the bad block generated during a flash operation to an unused spare block found through the resident mapping information, updating the resident mapping information as updated mapping information, and recording the updated mapping information in the block map page belonging to the block map page.