A differential amplifier circuit and a frequency mixer for improving linearity are disclosed. The disclosed differential amplifier circuit includes first and second loads, a first output terminal for the first load, a second output terminal for the second load, a differential amplifying stage including a differential stage for amplifying a voltage difference between a first input stage and a second input stage, and a biasing current source for biasing the differential stage, and a non-linearity filtering circuit for filtering a non-linear signal generated from the differential amplifying stage. The non-linearity filtering circuit includes a first cross circuit including a first transistor to connect the first and second output terminals, and a second cross circuit including a second transistor to connect the first and second output terminals. The differential amplifier circuit achieves an improvement in linearity, as compared to conventional differential amplifier circuits, by offsetting, at a load side, a non-linear component generated at an active element of the differential amplifier circuit, to output only a linear current component.