A game machine includes a CPU and, when a game cartridge is loaded in the game machine, the CPU is electrically connected to a ROM in the game cartridge and an electronically erasable non-volatile flash memory having at least two game data storage backup areas. Game data generated during the progress of a game is maintained in a volatile work memory and, in response to an instruction provided by a user, an attempt to save this data (referred to herein as "last" game data or as the "latest" game data) in an appropriate backup storage area of a non-volatile flash memory is made. Whenever the user instructs the game machine to save a game, the CPU compares the write age of each backup area and selects a game data backup area that is stored with game data having an oldest write age. Because electronically erasable non-volatile memories become less reliable and susceptible to degradation and failure after repeated usage, the CPU attempts a writing of the game data to the selected backup area, and then immediately performs a check to determine if the write operation to the selected backup area was successfully performed. If writing to the selected backup area can not be successfully performed after a predetermined number of repeated attempts, for example, due to memory element defect or an abrupt failure of memory area, and only a single other remaining backup storage area containing older game data is available, a writing of the latest game data over the game data from a previous gaming session which was stored in that single remaining backup storage area is precluded (i.e., prohibited), so as to always leave intact at least one area of older saved game data that was generated during the preceding game play session. Writing to the selected backup area to save the latest game data is prohibited if there are not at least two available and writable (i.e., non-defective) backup areas present in the non-volatile memory. In addition, the flash memory may be provided with flag storage areas for identifying "write prohibited" backup areas and "unwritable" backup areas.