A rail-to-rail amplifier for amplifying an analog signal from a DAC includes a first differential input section, which includes an n-channel transistor pair, a second differential input section, which includes a p-channel transistor pair, a first current supply provided between the second differential input section and a high voltage side supply, and a current controller for the second input section provided between the first current supply and the second differential input section for controlling the current supply to the second differential input section in accordance with data of a predetermined bit position in input digital data to the DAC. A second current supply is provided between a low voltage side supply and the first differential input section and a current controller for the first input section is provided between the second current supply and the first differential input section for controlling the current supply to the first differential input section in accordance with data of a predetermined bit position in input digital data to the DAC.