A current-mode filter includes a first, a second, and a third transistor having the same channel polarity. The drain of the first transistor is connected to the source of the second transistor functioning as a gate grounded circuit. The drain of the second transistor is connected to the gates of the first and third transistors. A first and a second capacitive element are connected to the gate and drain of the first transistor. The current source supplies a bias current to each of the first and second transistors. The drain of the first transistor is used as an input terminal. An output signal is extracted from a drain current of the third transistor. Therefore, only one transconductance adjustment circuit is enough.