A pitch control device for a coaxial double-rotor helicopter, configured to be located between an upper rotor hub and a lower rotor hub of the helicopter, the device comprising: a central shaft configured to be fixed so as to be immobile, and forming a stepped cross arm protruding from the middle part of said central shaft; an upper outer shaft provided above the cross arm on the outside of the central shaft, and configured to transmit drive to the upper rotor hub; a lower outer shaft provided below the cross arm on the outside of the central shaft, and configured to transmit drive from the lower rotor hub; a sector reversing gear mounted on an outer end of the cross arm via a bearing; a first conical gear provided at the upper end of the lower outer shaft, and meshing with a lower part of the sector reversing gear; a second conical gear provided at the lower end of the upper outer shaft and meshing with an upper part of the sector reversing gear; an upper variable pitch ring above the second conical gear, and configured to move up and down along the central shaft; a lower variable pitch ring below the first conical gear, and configured to move up and down along the central shaft; an upper swash plate above the upper variable pitch ring, and configured to be hinged with the upper rotor hub via a first connecting rod; a lower swash plate below the lower variable pitch ring, and configured to be hinged with the lower rotor hub via a second connecting rod; a first rocker extending out from the upper variable pitch ring, with an outer end of the first rocker hinged with the upper swash plate via a third connecting rod; a second rocker extending out from the lower variable pitch ring, with an outer end of the second rocker hinged with the lower swash plate via a fourth connecting rod; a gear box to which the outer end of the cross arm at the middle part of the central shaft is connected, wherein the first conical gear, the second conical gear, and the sector reversing gear are inside the gear box; a main steering gear connected to the outside of the gear box, and hinged with middle parts of the first rocker and the second rocker via respective upper and lower output shafts which are configured to move in the same direction; a course steering gear connected to the outside of the gear box, and having upper and lower output shafts which are configured to move in the opposite directions; an upper rocker having a first end part hinged to the upper output shaft of the course steering gear, a second, opposite, end part hinged with the upper variable pitch ring and a middle part hinged on the gear box; a lower rocker having a first end part hinged to the lower output shaft of the course steering gear, a second, opposite, end part hinged with the lower variable pitch ring, and a middle part hinged on the gear box. a central shaft configured to be fixed so as to be immobile, and forming a stepped cross arm protruding from the middle part of said central shaft; an upper outer shaft provided above the cross arm on the outside of the central shaft, and configured to transmit drive to the upper rotor hub; a lower outer shaft provided below the cross arm on the outside of the central shaft, and configured to transmit drive from the lower rotor hub; a sector reversing gear mounted on an outer end of the cross arm via a bearing; a first conical gear provided at the upper end of the lower outer shaft, and meshing with a lower part of the sector reversing gear; a second conical gear provided at the lower end of the upper outer shaft and meshing with an upper part of the sector reversing gear; an upper variable pitch ring above the second conical gear, and configured to move up and down along the central shaft; a lower variable pitch ring below the first conical gear, and configured to move up and down along the central shaft; an upper swash plate above the upper variable pitch ring, and configured to be hinged with the upper rotor hub via a first connecting rod; a lower swash plate below the lower variable pitch ring, and configured to be hinged with the lower rotor hub via a second connecting rod; a first rocker extending out from the upper variable pitch ring, with an outer end of the first rocker hinged with the upper swash plate via a third connecting rod; a second rocker extending out from the lower variable pitch ring, with an outer end of the second rocker hinged with the lower swash plate via a fourth connecting rod; a gear box to which the outer end of the cross arm at the middle part of the central shaft is connected, wherein the first conical gear, the second conical gear, and the sector reversing gear are inside the gear box; a main steering gear connected to the outside of the gear box, and hinged with middle parts of the first rocker and the second rocker via respective upper and lower output shafts which are configured to move in the same direction; a course steering gear connected to the outside of the gear box, and having upper and lower output shafts which are configured to move in the opposite directions; an upper rocker having a first end part hinged to the upper output shaft of the course steering gear, a second, opposite, end part hinged with the upper variable pitch ring and a middle part hinged on the gear box; a lower rocker having a first end part hinged to the lower output shaft of the course steering gear, a second, opposite, end part hinged with the lower variable pitch ring, and a middle part hinged on the gear box.