Provided is a fiber laser generating Terahertz wave. The fiber laser comprises: a light source generating a laser beam as a pump light; first and second resonators first and second resonators first and second resonators resonating the laser beam into first and second wavelengths; and a coupler separating and supplying the laser beam generated in the light source to the first and second resonators and again feeding back the laser beam having the first and second wavelengths resonated respectively in the first and second resonators to the light source.