Abstract We have observed reflection high energy positron diffraction (RHEPD) using the electrostatic positron beam apparatus, where positrons were accelerated at 20 keV and converged using three einzel lenses and a collimator. To reduce beam energy dispersion and gamma ray background, a 45° electrostatic prism and einzel lenses were newly added to the original apparatus. The positron beam is further collimated to 1 mm diameter. Final beam energy dispersion and angular divergence are less than 0.1 keV and 0.1°, respectively. Any noises arising from the gamma rays are not observed. We also fabricated the positron beam observation system with a dynamic range of approximately 4.3×109. The above improvements enabled to detect the fine structures of diffraction patterns and rocking curves.