Abstract A small-scale test stand of a negative NBI source composed of a prototype negative ion source, an RF generator, and an HV power supply for negative ion beam extraction has been established. The magnetic filter and a beam extraction grid system with electron deflection magnets were designed for the prototype negative ion source. The BL value of the magnetic filter is 1.6 mTm and almost all electrons are deflected onto the surface of the extraction grid. The first negative ion beam extraction experiments have been carried out. When the extraction voltage is 5.6 kV, the negative ion current density is 0.6 mA/cm2 at 5 kW RF power. The e/H− ratio is about 2–3 and it decreased below 1 when the electrical potential of the plasma bucket is grounded.