To provide a read-only semiconductor memory capable of reducing power consumption after suppressing the increase of a circuit scale and an obstruction in making the memory highly integratable.

Storage information of memory cells 2 and the flag memory cell 5 connected to the word line selected by a row address signal X appear on corresponding bit lines. Bit lines equivalent to one word are selected by a bit line selection means 13 receiving a column address signal Y and the storage information of selected memory cells 2 appear on signal lines 19(0)-19(31) and, also, a bit line for flag is selected by a bit line for flag selection means 20 and the storage information of a selected flag memory cell appear on a signal 25. Then, exclusive ORs of information appeared on respective signal lines 19 and information appeared on the signal line 25 are calculated in respective output parts 28(0)-28(31) of an output circuit 27. These calculated results are outputted as read-out data from data output lines DL0-DL31.