A buffer circuit having high slew rate is provided. The buffer circuit is provided, which includes a plurality of transistors having the same conductivity type and a capacitor and whose gain is determined depending on the gain of all the plurality of transistors. A buffer circuit having high driving capability and high gain of a high-frequency component can be provided. Such a buffer circuit has also high slew rate. The plurality of transistors having the same conductivity type in the buffer circuit may be either p-channel transistors or n-channel transistors.