A double-sided polishing apparatus includes: a lower surface plate; an upper surface plate; and a carrier disposed between the lower surface plate and the upper surface plate and holding a disk-shaped workpiece, wherein the carrier is configured to rotate about a center of the lower surface plate and the upper surface plate and to rotate about a center of the carrier, the double-sided polishing apparatus includes a thickness measuring sensor at a fixed position above the upper surface plate or below the lower surface plate or at a movable position in an upper portion of the upper surface plate or a lower portion of the lower surface plate, the carrier includes circular perforations each holding the workpiece at a position eccentric to the center of the carrier, when a central position of any of the perforations preset by a user is defined as a first reference position, with a distance between a center of the upper surface plate or the lower surface plate and a center of any of the perforations preset by the user being shortest or longest, and a position apart from the first reference position by half of a first distance in a direction of the center of the carrier is defined as a second reference position, with the first distance being a predetermined length within 30% of a radius of the perforation, then the thickness measuring sensor is provided in a range of the first distance about the second reference position in a plan view, and the thickness measuring sensor is configured to measure a thickness of the workpiece in a state in which the workpiece is held in the perforation, through a measuring hole provided on the upper surface plate or the lower surface plate closer to a side on which the thickness measuring sensor is disposed.