Large parity-violating longitudinal single-spin asymmetries A^<e+>_<L> = 0.86^<+0.30>_<-0.14> and A^<e->_<L> = 0.88^<+0.12>_<-0.71> are observed for inclusive high transverse momentum electrons and positrons in polarized p + p collisions at a center-of-mass energy of √s = 500 GeV with the PHENIX detector at RHIC. These e± come mainly　from the decay of W± and Z0 bosons, and their asymmetries directly demonstrate parity violation in the couplings of the W± to the light quarks. The observed electron and positron yields were used to estimate W± boson production cross sections for the e± channels of ð(pp → W+X) × BR(W+ → e+ve) = 144.1 ± 21.2(stat)^<+3.4>_<-10.3>(syst) ± 21.6(norm) pb, and ð(pp → W-X) × BR(W- → e-v^^-e) = 31.7 ± 12.1(stat)^<+10.1>_<-8.2>(syst) ± 4.8(norm) pb.