A mounting device for mounting a microphone on a musical instrument includes a holder adapted to hold the microphone and having a rod, and a clamping unit. The clamping unit includes a seat mounted on the rod, a pair of spaced-apart first and second clamp arms which is adapted to clamp a peripheral edge of the musical instrument and which are converged to form a common connection part connected to the seat, a shaft extending through the first and second clamp arms and having one end portion extending outwardly of the first clamp arm, and a nut threadedly engaging the shaft to bias the first clamp arm toward the second clamp arm.