1. A flash memory having a memory cell array composed of a plurality of user areas each for storing data and a plurality of flag areas each for indicating a state of said each user area, comprising: a state information generator for generating state information that indicates a state of said each user area by referring to said each flag area, said state information noticing said state to the outside; and an output unit for outputting said state information wherein said state information generator calculates a ratio of invalid states of said user areas by referring to said flag areas and compares the calculated ratio with a pre-stored predetermined ratio, and wherein said state qenerator compares the pre-stored predetermined ratio with said ratio of invalid user areas, and if said ratio is larger than the predetermined ratio, generating said state information that indicates a garbage collection process is necessary.