A new type of end‐loss‐ion energy analyzer (ELA; a multigridded Faraday cup) is applied to measure plasma ion temperaturesTipand plasma potentials &Fgr;Pin the GAMMA 10 tandem‐mirror device. As compared with conventional‐type ELA, this new ELA has obliquely placed ion‐ and secondary‐electron‐repeller grids and a collector plate with respect to external tandem‐mirror magnetic fields. One of the most useful capabilities of this new ELA for precise ion measurements is to greatly reduce the current of high‐energy electrons onto the collector plate. Also, this compact‐sized ELA is scannable in the plasma to obtain radial profiles ofTipand &Fgr;Pwithout providing any perturbations of the tandem‐mirror magnetic fields because it neither adds its own magnetic field nor needs to shield against the ambient magnetic field. Ion trajectories in the new ELA are numerically calculated so as to make a further understanding of its physics principles and to optimize its design. The energy‐calibration experiments for the new ELA are carried out using ion beams; a fairly good agreement in the analyzed beam energies from the new ELA data and from conventional‐type ELA data is attained. Furthermore, the first application of the new ELA to plasma diagnostics is made; a substantial reduction in energetic‐electron influxes onto real ion signals makes a significant improvement in the analyses ofTipand &Fgr;P.