An oscillating device for a superfinishing device comprising: a driving source; a grindstone which performs an oscillating motion; and a connecting mechanism which converts a rotational motion of the driving source into an oscillating motion and transmits the oscillating motion to the grindstone, wherein the connecting mechanism includes: a connecting rod mounted a spindle, to which the rotation of the driving source is transmitted, and configured to perform eccentric motion with respect to a rotary shaft of the spindle, a connecting arm connected to the connecting rod, a connecting shaft mounted on the connecting arm, wherein the connecting arm is configured to oscillate around an axial line of the connecting shaft and the connecting shaft is configured to reciprocally rotate around the axial line thereof, and a grindstone holder mounted on a tip of the connecting shaft; characterized in that the connecting rod includes a component provided with a tubular body made of a fiber-reinforced resin; the tubular body comprises a hollow portion; the tubular body includes a first through hole (11, 15a) for inserting a shaft eccentric to the rotary shaft of the spindle therethrough, and a second through hole (12, 16a) for connecting the connecting arm thereto; wherein blocks (18, 19) made of a fiber-reinforced resin are inserted into openings at opposite ends of the tubular body to close the openings; and the first through hole (11, 15a) and the second through hole (12, 16a) are formed to penetrate through the tubular body and the blocks (18, 19). a driving source; a grindstone which performs an oscillating motion; and a connecting mechanism which converts a rotational motion of the driving source into an oscillating motion and transmits the oscillating motion to the grindstone, wherein the connecting mechanism includes: a connecting rod mounted a spindle, to which the rotation of the driving source is transmitted, and configured to perform eccentric motion with respect to a rotary shaft of the spindle, a connecting arm connected to the connecting rod, a connecting shaft mounted on the connecting arm, wherein the connecting arm is configured to oscillate around an axial line of the connecting shaft and the connecting shaft is configured to reciprocally rotate around the axial line thereof, and a grindstone holder mounted on a tip of the connecting shaft; characterized in that the connecting rod includes a component provided with a tubular body made of a fiber-reinforced resin; the tubular body comprises a hollow portion; the tubular body includes a first through hole (11, 15a) for inserting a shaft eccentric to the rotary shaft of the spindle therethrough, and a second through hole (12, 16a) for connecting the connecting arm thereto; wherein blocks (18, 19) made of a fiber-reinforced resin are inserted into openings at opposite ends of the tubular body to close the openings; and the first through hole (11, 15a) and the second through hole (12, 16a) are formed to penetrate through the tubular body and the blocks (18, 19). a connecting rod mounted a spindle, to which the rotation of the driving source is transmitted, and configured to perform eccentric motion with respect to a rotary shaft of the spindle, a connecting arm connected to the connecting rod, a connecting shaft mounted on the connecting arm, wherein the connecting arm is configured to oscillate around an axial line of the connecting shaft and the connecting shaft is configured to reciprocally rotate around the axial line thereof, and a grindstone holder mounted on a tip of the connecting shaft; characterized in that the connecting rod includes a component provided with a tubular body made of a fiber-reinforced resin; the tubular body comprises a hollow portion; the tubular body includes a first through hole (11, 15a) for inserting a shaft eccentric to the rotary shaft of the spindle therethrough, and a second through hole (12, 16a) for connecting the connecting arm thereto; wherein blocks (18, 19) made of a fiber-reinforced resin are inserted into openings at opposite ends of the tubular body to close the openings; and the first through hole (11, 15a) and the second through hole (12, 16a) are formed to penetrate through the tubular body and the blocks (18, 19).