To configure the yaw axis control mechanism of a coaxial counter-rotating unmanned helicopter to be able to accurately control the pitch angle of the upper rotor blade by a simple configuration even if the precise adjustment is not performed. A rudder control rod is inserted into a main mast of a coaxial counter-rotating helicopter, a lower end portion thereof is connected to an output lever of the rudder servo, and a mixing rod head is fixed to an upper end portion. A link mechanism connected to the upper swash plate is attached to a side surface portion of the mixing rod head, the vertical displacement of the mixing rod head moving up and down together with the rudder control rod is converted into a displacement for tilting an upper blade holder around the spindle via the link mechanism, thereby changing the pitch angle of the upper rotor blades.