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Two‐dimensional ion velocity distribution functions are measured in electron cyclotron resonance (ECR) argon plasmas under a divergent magnetic field configuration using a directional analyzer. Ions produced in the ECR source grow to a beam in the downstream region inside an allowed angle, while the distribution function is almost isotropic outside the angle. The beam energy corresponds to the potential difference between the ECR source and downstream locations. The ion beam is almost parallel to an applied magnetic field, the beam being deflected along the divergent magnetic field lines. The energy spread and the temperature of the ion beam, and the temperature of the bulk ions are also shown as a function of the distance from the ECR source or of the gas pressure. The validity of the directional analyzer measurements is discussed by considering the motion of an ion in a sheath in front of the analyzer.