A transmission device for a hybrid aircraft comprising a turboshaft engine including a gas generator, a free turbine, and a main rotor, the device comprising a first reversible electric machine coupled to a shaft of the free turbine by way of a first deactivatable coupling means, and to the main rotor, and a second reversible electric machine coupled to a shaft of the gas generator by way of a second deactivatable coupling means, and coupled to the main rotor by way of a third deactivatable coupling means, the second deactivatable coupling means being able to be activated when the second electric machine rotates in a first direction of rotation, and the third deactivatable coupling means being able to be activated when the second electric machine rotates in a second direction of rotation opposite to the first direction of rotation.