A differential amplifier achieving a high throughput rate with reduced power consumption includes a differential circuit (1), output circuit (2), a constant current source transistor (21), a drive transistor (3), and a switching circuit (4). A difference voltage (V x ) relative to a difference between voltages applied to non-inverting and inverting inputs of the differential circuit (1) is applied to the switching circuit (4). The switching circuit (4) supplies a drive signal to the drive transistor (3) to enable the drive transistor (3) when the difference voltage (V x ) is below a predetermined threshold voltage (V T ), and to disable the drive transistor (3) when the difference voltage (V x ) is above the predetermined threshold voltage.