A double side polishing apparatus comprises an upper polishing plate and a lower polishing plate for polishing both sides of a wafer; a plurality of carriers, each including a center plate and a circumferential plate, the center plate having a mounting hole where the wafer is mounted, the circumferential plate having a fitting hole where the center plate is fitted and a gear part formed along the outer periphery thereof, the center of the mounting hole being eccentric from the center of the center plate, the center of the fitting hole being eccentric from the center of the circumferential plate; and a sun gear and an internal gear engaged with the gear part to transmit a rotational force to the plurality of carriers, wherein a fitting direction of a center plate into a fitting hole is adjustable for at least two carriers among the plurality of carriers.