This paper proposes a second-order differential microphone array (DMA) that can continuously steer in the main lobe direction. First, a general response of the second-order DMA is derived as a linear combination of a monopole and dipoles. Nine- and seven-microphone systems are proposed to realize continuous steering of the second-order DMA. The proposed system synthesizes the steered beam pattern without requiring the phase shifter by using back-to-back cardioids. Simulation results show that the nine-microphone configuration yields a nearly constant and high white noise gain, but the seven-microphone configuration has the practical advantage that it requires fewer microphones.