Buffer circuit and integrated circuit

In a two-stage inverter circuit including an inverter circuit constituted by first and second FETs and an inverter circuit constituted by two FETs, a source and a gate of a third FET are connected to a first power source and a second power source, respectively. A drain of the third FET is connected to a source of the first FET. A source and a gate of a fourth FET are connected to the first power source and the second power source, respectively. A drain of the fourth FET is connected to a source of a seventh FET. A gate of the seventh FET is connected to the second power source, and a drain of the seventh FET is connected to a back gates of the first, third, fourth, seventh and fifth FETs. The drain of the third FET is connected to the drain of the fourth FET.