A tunable filtering device comprising a base; first and second optical fibers aligned and facing each other; a tunable filter installed on the optical path between the first and second optical fibers, for transmitting only a beam of a specific wavelength from the beam emitted from the first optical fiber toward the second optical fiber; an actuator driving the tunable filter; a beam splitter installed on the optical path between the tunable filter and the second optical fiber, for reflecting a portion of the beam transmitted through the tunable filter and transmitting the rest; an auxiliary optical fiber installed on the base, for receiving a beam reflected from the beam splitter for further transmission; and a controller detecting the beam transmitted through the auxiliary optical fiber and controlling the actuator according to the detected beam.