PURPOSE: To constitute on-chip memories having the number of words which are different from each other without changing entirely the basic constitution of a decoder and address buffer, by fixing the level of an appropriate part of a circuit for selecting and driving a word line.

CONSTITUTION: One of input signals of unit decoders DEC4WDEC7, to which the output signal a2 of a unit address buffer ADB3 is supplied, is always set to a low level. Therefore, the outut of an AND circuit, namely unit decoder among DEC4WDEC7 is set to a low level irrespectively of other buffer outputs a0, a1(-a0, -a1) corresponding to address signals A0 and A1, and word lines W4W W7 below a dashed line C-C are not selected. In addition, by setting the input of a unit address buffer ADB3 to a low level, it is possible that a half of the word lines W0WW7, namely, memory cells below the dashed line C-C cannot be selected.