An ultrasonic resonator support structure including a holder supports an ultrasonic resonator at both sides such that the ultrasonic resonator is rotatable to the holder. The ultrasonic resonator includes an ultrasonic horn with a machining tool attached, and a first booster and a second booster coaxially fixed one by one to both ends in the axial directions of the ultrasonic horn. The holder has a rolling bearing mechanism that rotatably supports the first booster side of the ultrasonic resonator and a gas bearing mechanism that rotatably supports the second booster side of the ultrasonic resonator.