33 has a threshold voltage vth higher than the normal one the increased amount of the threshold voltage is dvth 1 2 u00d7 vbs when the supply voltage vdd is 5 0 v and the back gate of the n mos transistor 33 is connected to the source of the n mos transistor 33 for example a voltage signal having a voltage of 3 5 v to 3 0 v is output from the source of the n mos transistor 33 having a threshold voltage vth of 1 5 v to 2 0 v since the back gate of the n mos transistor 33 is connected to the ground voltage gnd in this embodiment the increased amount of the threshold voltage dvth 1 2 u00d7 3 5 v to 1 2 u00d7 3 0 v 0 94 v to 0 87 v should be taken into consideration accordingly a voltage signal of 5 0 v vth 5 0 v 1 5 0 94 v to 5 0 v 2 0 0 84 v 2 56 v to 2 23 v is output from the source of the n mos transistor 33 when the supply voltage vdd is 3 0 v and the back gate of the n mos transistor 33 is connected to the source of the n mos transistor 33 a voltage signal of 1 5 v to 1 0 v is output from the source of the n mos transistor 33 the increased amount of the threshold voltage dvth 1 2 u00d7 1 5.