Characteristics and performance of the recently developed volume H−ion source and the helical electro‐static quadrupole (HESQ) at KEK are described. Observation of the H−beam intensity enhancement by introducing a small amount of cesium vapor is shown. The extracted H−beam current of 20 mA was obtained in the cesium‐mode operation. The measured 90% normalized beam emittance was about 1 &pgr;mm.mrad for 12 mA beam. We found that the workfunction of the plasma electrode surface which was decreased by cesium coverage had an important role to enhance the H−beam intensity. A helical electro‐static quadrupole (HESQ) for focusing low energy and high current negative ion beams has been developed at KEK. Various negative ions such as Cu−and Au−ion beams of more than several mA have been transported and focused with the HESQ. Comparison of the focused beam emittance between measurements and calculations are presented.