In order to realize long-lived electric propulsion systems, we have been investigating an electrodeless plasma thruster. In our concept, high-density helicon plasma is accelerated by a magnetic nozzle for thrust production. In order to improve the thrust performance with simple systems, high magnetic flux density magnetic nozzle formed by permanent magnets is employed to our laboratory model plasma thruster. A magnetic circuit, which has high magnetic flux density up to 0.2 T at the magnetic nozzle throat, is constructed by permanent magnets and magnetic yoke. In order to investigate the thrust performance of this thruster, the thrust force is measured by a torsion-pendulum type thrust stand. From the thrust measurement, the thrust force and specific impulse increases with the RF power input. The thrust efficiency is drastically improved by increasing the RF power input, and it is considered to be caused by the discharge mode transition from the CCP to the ICP . The maximum thrust force and thrust efficiency of 2.7 ± 0.4 mN and 0.26 % is measured when the Ar gas mas flow rate is 1.2 mg/s, and plasma production frequency and power is 13.56 MHz and 1000 W. NomenclatureA e = area of thruster exit F diamag = electromagnetic thrust force F thermal = pressure force F total = total thrust force g 0 = acceleration of gravity I sp = specific impulse k B = Boltzmann constant m n = mass of neutral particle m & = injected mass flow rate 2 eff m & = effective mass flow rate ing m & = ingested mass flow rate P c = pressure of vacuum chamber P source = RF power for plasma production T n = temperature of neutral gas (assumed to be 300 K) ∆t = pulse width δ = displacement η = thrust efficiency