The present cupping device attaches to the harmonica holder and provides a simulated cupping effect when the musician is playing the harmonica hands-free. The cupping device is generally a U-shaped elongate channel formed by bending a rigid sheet material to create a chamber. The elongate channel attaches to a harmonica holder and the open side of the elongate channel receives the back of a harmonica also mounted on the harmonica holder. Each end of the elongate channel is open to permit the ingress and egress of air while playing. A microphone may be clipped to one or both open ends and positioned within the elongate channel. The cupping device isolates the harmonica sound so that it can be amplified at higher volumes without feedback or interference.