PURPOSE: To contrive multi-values of information storage, to reduce the number of transistors and to contrive the accelerating of a writing time.

CONSTITUTION: Threshold values of a memory transistor are set at three kinds of values or more in a nonvolatile semiconductor memory. This memory is provided with the memory transistor MT constituted of a source area S and a drain area D of a second conduction type provided on a first conduction type semiconductor substrate 11 and a floating gate electrode FG and a control gate electrode CG provided successively on an area striding over the source area S and the drain area D via an insulation film 12. The threshold value Vth of the memory transistor MT is controlled by the potentials of the floating gate electrode FG and the control gate electrode CG. Further, an electric charge injection control means 13 controlling quantity of electric charge to be injected into the floating gate electrode FG is provided. The electric charge injection control means 13 performs the injection control of electric charge quantities of two kinds or more with respect to the floating gate electrode FG at the time of a writing operation.