A double-side polishing apparatus, comprising: a lower surface plate in a ring-like shape, which has an upper surface formed into a polishing surface, and which is supported on a base; an upper surface plate which has a lower surface formed into a polishing surface, and which is provided vertically movably and rotatably around a first rotary shaft, above the lower surface plate; a carrier which is disposed between the lower surface plate and the upper surface plate and which has a through-hole that holds a work; an upper surface plate rotation driving mechanism that includes a lathe dog which is fixed to the first rotary shaft and with which the upper surface plate is engaged in a free up-and-down motion, and that rotationally drives the upper surface plate; wherein the first rotary shaft rotating the upper surface plate has a cylindrical shape, is rotatably inserted in a central hole of the lower surface plate and extends vertically, and has the lathe dog fixed to an upper end thereof; the double-side polishing apparatus further comprising: carrier rotation driving mechanism that includes a sun gear which is disposed in a central hole of the lower surface plate, which meshes with the carrier and rotates around a second rotary shaft, and an internal gear which is disposed around the lower surface plate and meshes with the carrier, and that causes the carrier to revolve around the sun gear while rotating the carrier on its axis; and a driving mechanism that rotationally drives the second rotary shaft, the double-side polishing apparatus being characterized in that; the second rotary shaft rotating the sun gear is rotatably inserted through the first rotary shaft, which has a cylindrical shape, is used for driving the upper surface plate and extends vertically, and the second rotary shaft has a pinion gear fixed to an upper end thereof; the sun gear has a cylindrical shape and is rotatably supported outside an upper end part of the first rotary shaft used for driving the upper surface plate, and the sun gear has an internal tooth formed on an inner circumference part and an external tooth that meshes with the carrier, formed on an outer circumference part; and a void part is formed at an upper part of the first rotary shaft for driving the upper surface plate, and in the void part, a planetary gear which meshes with the pinion gear being provided on the second rotary shaft and the internal tooth of the sun gear and which transmits rotation of the second rotary shaft rotated by the driving mechanism to the sun gear, is disposed. carrier rotation driving mechanism that includes a sun gear which is disposed in a central hole of the lower surface plate, which meshes with the carrier and rotates around a second rotary shaft, and an internal gear which is disposed around the lower surface plate and meshes with the carrier, and that causes the carrier to revolve around the sun gear while rotating the carrier on its axis; and a driving mechanism that rotationally drives the second rotary shaft, the double-side polishing apparatus being characterized in that; the second rotary shaft rotating the sun gear is rotatably inserted through the first rotary shaft, which has a cylindrical shape, is used for driving the upper surface plate and extends vertically, and the second rotary shaft has a pinion gear fixed to an upper end thereof; the sun gear has a cylindrical shape and is rotatably supported outside an upper end part of the first rotary shaft used for driving the upper surface plate, and the sun gear has an internal tooth formed on an inner circumference part and an external tooth that meshes with the carrier, formed on an outer circumference part; and a void part is formed at an upper part of the first rotary shaft for driving the upper surface plate, and in the void part, a planetary gear which meshes with the pinion gear being provided on the second rotary shaft and the internal tooth of the sun gear and which transmits rotation of the second rotary shaft rotated by the driving mechanism to the sun gear, is disposed. the second rotary shaft rotating the sun gear is rotatably inserted through the first rotary shaft, which has a cylindrical shape, is used for driving the upper surface plate and extends vertically, and the second rotary shaft has a pinion gear fixed to an upper end thereof; the sun gear has a cylindrical shape and is rotatably supported outside an upper end part of the first rotary shaft used for driving the upper surface plate, and the sun gear has an internal tooth formed on an inner circumference part and an external tooth that meshes with the carrier, formed on an outer circumference part; and a void part is formed at an upper part of the first rotary shaft for driving the upper surface plate, and in the void part, a planetary gear which meshes with the pinion gear being provided on the second rotary shaft and the internal tooth of the sun gear and which transmits rotation of the second rotary shaft rotated by the driving mechanism to the sun gear, is disposed.