We demonstrate an amplification of a microwave signal by a strongly driven two-level system in a coplanar waveguide resonator. The effect known from optics as dressed-state lasing is observed with the single quantum system formed by a persistent current (flux) qubit. The transmission through the resonator is enhanced, when the Rabi frequency of the driven qubit is tuned into resonance with one of the resonator modes. The amplification as well as linewidth narrowing of the weak probe signal has been observed. The laser emission at the resonator fundamental mode has been studied by measuring the emission spectrum. We analyze our system and found an excellent agreement between the experimental results and the theoretical predictions, obtained in the frame of the dressed-state model.