are in non write status the input sin1 of the sensing circuit 14 is discharged by the selected memory device and becomes low level low potential at the input sin1 of the sensing circuit 14 causes the output vo1 of the inverter circuit inv11 to be high level and the n channel type mos fet mn11 to become conductive accordingly the output vsa1 of the sensing circuit 14 is at low level at this point the gate of the n channel type mos fet mn13 also becomes high level however since the selected memory device and the reference memory device have the same characteristics the input sin1 of the sensing circuit 14 and the input rin1 of the reference voltage generation circuit 15 are at the same low voltage level this results in no current flow via the n channel type mos fet mn13 accordingly the output vsa1 of the sensing circuit 14 and the output vra1 of the reference voltage generation circuit 15 are both at low level on the other hand if the selected memory device is in write status the input sin1 of the sensing circuit 14 is charged via the p channel type mos fet mp11 and the n channel type mos fet mn11 and becomes high level increase of the potential at the input sin1 of the sensing circuit 14 causes the output vo1 of the inverter circuit inv11 to be low this results in that the n channel type.