A tremolo operating mechanism comprising an arm socket secured onto a base plate, a resin bushing contained in the upper part of the arm socket, a torque adjusting screw screwed into the upper part of the arm socket to press the resin bushing, and an arm receiving resin nut which is engaged with the lower part of the arm socket and is also engaged with the lower end portion of a tremolo arm. The tremolo arm rotates on the shaft thereof to change the amount of screw engagement with the arm receiving resin nut and adjust the height of the tremolo arm from the body. As the torque adjusting screw rotates, the torque of the tremolo arm is adjusted by the resin bushing. Since the tremolo arm is supported by the resin bushing and the arm receiving resin nut, it does not interfere with the arm socket to improve operability.