The 1/3‐scaled H−ion source for NBI‐system of Large Helical Device has been developed. By seeding cesium vapor into the multicusp plasma source, the H−ion current is enhanced 3 times larger than that in pure hydrogen operation. The reduction of electron current and operating gas pressure is also observed. Total H−ion current of 8.5 A has been obtained from 800 extraction holes of 9 mm in diameter arranging in a large area of 25×50 cm2. The ratio of electron to H−ion current can be reduced to 2 by using the EggBox Cell placed on the plasma grid. From 36 extraction holes, the H−ion current of 1.24 A has been obtained with the extraction voltage of 8.5 kV, which corresponds to the current density of 54 mA/cm2. The H−ion current density increases as an extraction voltage and an input arc power increase.