PURPOSE: To attain storing in an excellently fixed capacity of memory with a single operation by supplying an AC voltage to a control electrode and a voltage to be stored in an injection area at the same time.

CONSTITUTION: On a p-type semiconductor base substance 1, three n-type diffusion parts 2, 8, and 9 are formed, and each composes an injection area on one hand, and a source and a drain of a read-out transistor on the other hand. And an equal voltage to a voltage which should be substantially stored in an electrode 22 connected with the injection area 2 is supplied, and at the same time, such an AC voltage is supplied to a control electrode as decreases an amplitude from a higher value than a critical value Acrit and generates a change in electric charges of a floating gate. Thus, an analog value expressed in a voltage form can be stored easily and accurately.