The average polarization of the nucleus A2B (bound state) produced in the polarizedmuon capture reaction 12C (,,-v ~12B ,,~ , ~, was measured by the muon spin resonance method in a pulsed muon beam. The polarization of ~2B was maintained completely under a magnetic field of 3 kG in a Grafoil target. After the observed result was corrected for the contribution from the excited states of 12B, P,v (ground state) was +2.4 deduced to be 0.462+0.053. This result yields ge/gA=lO.l_2.6, which is almost consistent with the PCAC prediction. Nuclear Reactions muon capture t# , ~) ; measured P of t2B; deduced pseudoscalar form factor in weak hadronic current.