An electron cyclotron current drive by the fundamental O-mode is numericallyanalysed in the off-axis region of a reactor-grade tokamak. By scanning thelaunching direction in both the toroidal and poloidal directions, the optimumdirection of beam injection is obtained to drive a current with a maximumvalue of I/ρw at the desired magnetic surface, where I is thetotal driven current and ρw is the radial width of the drivencurrent. When the current is driven at the position where a ray trajectorybecomes tangent to the magnetic surface (referred to as the `tangentialresonance'), Doppler broadening of the current profile is significantlyreduced and I/ρw reaches a maximum value. In the case oftangential resonance, the driven current width is mainly determined by theeffects of the beam divergence and finite spatial width of the beam at thelaunching position. The width of the driven current is kept in a range of2-5% of the minor radius under the assumption of a beam divergence witha full angle of 2°. The dependence of the driven current on both thelocation of beam injection and the wave frequency is also examined.