[en] The ion flux density from the anode cup of a duoplasmatron type ion source was measured under the same conditions as the source operation with a special double probe. The ion flux density of 2.64×10¹⁸n/cm² sec was obtained at the source pressure of 460μ. Torr., the arc current of 1.0 amp. and the magnetic field strength of 1100 gauss. The ion flux density is almost proportional to the arc current, the area of the anode aperture and the magnetic field strength in the region below 2000 gauss. Above this region of the magnetic field the saturation effect was observed. The ion flux density has a maximum value at the source pressure of about 200μ Torr. and decreases quickly at higher pressure side, but slightly at lower pressure side. (author)