We propose the JHF-Kamioka neutrino experiment to study the mass and mixing of leptons to great precision through neutrino oscillation. The experiment uses a high intensity narrow-band neutrino beam produced by JHF, Japan Hadron Facility, and the world largest water Cherenkov detector, Super-Kamiokande. The main physics goals are: (1) to discover v(mu) --> v(e) oscillation with a mixing angle, theta(13), down to 0.006, (2) to measure the oscillation parameters in v(mu) --> v(mu) oscillation with a precision of 1% for the mixing angle and 10(-4)e-V-2 for the mass square difference, and (3) to confirm v(mu) --> v(tau) or to eliminate v(mu) --> v(s) by measuring the neutral current events. The experiment can extend the physics potential to measure CP violation in neutrino oscillation for the CP-violation phase (delta) down to 10-20degrees, by upgrading the JHF accelerator to 4 MW and by constructing a new 1 Mton water Cherenkov detector, Hyper-Kamiokande. The experiment is planned to start in 2007 at the same time of completing the JHF accelerator complex. (C) 2003 Elsevier Science B.V. All rights reserved.