Device for regulating a rotational speed, referred to as rotational speed NG, of a shaft of a gas generator of at least one turboshaft engine of a rotorcraft, said rotorcraft comprising: - at least one main rotor for generating at least lift and/or propulsion of said rotorcraft in the air, - a member for controlling a collective pitch of the blades of said at least one main rotor, said control member allowing a control setpoint Cp of said collective pitch to be generated in order to collectively control an angular orientation of the blades with respect to a hub of said at least one main rotor, - at least one turboshaft engine that can rotate said at least one main rotor, said at least one turboshaft engine at least temporarily producing an engine torque TQ that is transmitted to said at least one main rotor, said engine torque TQ being variable according to said control setpoint Cp of said collective pitch of the blades of said at least one main rotor, and - measuring means for taking, at any time, a measurement of said engine torque TQ transmitted by said at least one turboshaft engine to said at least one main rotor, said regulation device generating at least one law for controlling a control setpoint of said rotational speed NG of said shaft of said gas generator of said at least one turboshaft engine, said at least one law for controlling said control setpoint of the rotational speed NG being dependent on a travel speed V of said rotorcraft in a substantially horizontal direction Y and on a height z of said rotorcraft with respect to the ground S, characterised in that said regulation device comprises: - input means that can be connected to the measuring means, said input means allowing said regulation device to receive and analyse said measurement of said engine torque TQ, - at least one storage unit for storing a first threshold value TQ1 of said engine torque and a second threshold value TQ2 of said engine torque, said second threshold value TQ2 being selected so as to be greater than said first threshold value TQ1, and - a calculation unit for comparing said measurement of said engine torque TQ with said first and second threshold values TQ1 and TQ2, said calculation unit generating at least two laws NG1 and NG2 for controlling said control setpoint of rotational speed NG, said at least two control laws NG1 and NG2 being different from one another and dependent on said measurement of said engine torque TQ, a first control law NG1 being implemented at least when said measurement of said engine torque TQ is less than said first threshold value TQ1 and a second control law NG2 being implemented at least when said measurement of said engine torque TQ is greater than said second threshold value TQ2. - at least one main rotor for generating at least lift and/or propulsion of said rotorcraft in the air, - a member for controlling a collective pitch of the blades of said at least one main rotor, said control member allowing a control setpoint Cp of said collective pitch to be generated in order to collectively control an angular orientation of the blades with respect to a hub of said at least one main rotor, - at least one turboshaft engine that can rotate said at least one main rotor, said at least one turboshaft engine at least temporarily producing an engine torque TQ that is transmitted to said at least one main rotor, said engine torque TQ being variable according to said control setpoint Cp of said collective pitch of the blades of said at least one main rotor, and - measuring means for taking, at any time, a measurement of said engine torque TQ transmitted by said at least one turboshaft engine to said at least one main rotor, - input means that can be connected to the measuring means, said input means allowing said regulation device to receive and analyse said measurement of said engine torque TQ, - at least one storage unit for storing a first threshold value TQ1 of said engine torque and a second threshold value TQ2 of said engine torque, said second threshold value TQ2 being selected so as to be greater than said first threshold value TQ1, and - a calculation unit for comparing said measurement of said engine torque TQ with said first and second threshold values TQ1 and TQ2, said calculation unit generating at least two laws NG1 and NG2 for controlling said control setpoint of rotational speed NG, said at least two control laws NG1 and NG2 being different from one another and dependent on said measurement of said engine torque TQ, a first control law NG1 being implemented at least when said measurement of said engine torque TQ is less than said first threshold value TQ1 and a second control law NG2 being implemented at least when said measurement of said engine torque TQ is greater than said second threshold value TQ2.