We extrapolated observed photospheric magnetic field before the 3B/X1.2 flare occurred in NOAA 10486 on 2003 October 26. Two magnetic null points exist above the active region, which have no crucial role in triggering the flare, even though enhanced TRACE EUV/UV emission was observed before the main flare due to magnetic reconnection near the lower-altitude null point. We conclude that this flare results from the loss of equilibrium due to persistent flux emergence and photospheric motion, and strong shear. The accompanying fast CME with velocity of $\sim$ 800 km $s^{-1}$ shows quick mass pickup and energy increase in the low corona. Its kinetic energy is always larger than its potential energy.