The ion‐beam extraction performance of the 30‐kV–35‐A circular magnetic‐multipole bucket ion source applied for the neutral beam injection system of the Heliotron E fusion machine has been investigated with special reference to ion‐beam optics. By using the numerical simulation code for the cylindrical ion‐extraction system, the computational beam‐divergence angles have been compared with the experimental data. The experiments show that the applied three‐electrode beam optics are satisfactorily stable against source‐plasma variation and that the minimum beam‐divergence angle is less than 1.15 deg. The obtained optimal perveance of the ion source is nearly 6.3×10−6(A/V3/2), and the experimental optics behavior is in reasonable agreement with the numerical prediction. On the basis of the experiments, the effect of the edge angle of the first beam‐forming, high‐potential electrode is also discussed. The experiment suggests that the obtuse angle (∼73°) for that edge is preferable to the acute angle (∼30°).