1. A nonvolatile semiconductor memory device comprising a memory cell array for storing user data, provided by arranging a plurality of memory cells each provided with a variable resistive element including a first electrode, a second electrode, and a variable resistor made up of a metal oxide and sandwiched between the first electrode and the second electrode, wherein the metal oxide is an insulator in an initial state, resistance of the variable resistive element is decreased by a forming process, a resistance state of the variable resistive element changes between two or more different resistance states by application of a voltage between the first electrode and the second electrode after the forming process, the resistance state after being changed is maintained in a nonvolatile manner, and the variable resistive elements of all of the memory cells in the memory cell array are set to the highest resistance state of the two or more different resistance states in an unused state before the memory cell array is used to store the user data.