Nuclear structure of proton-rich unstable nucleus 28P has been studied by measuring its g-factor for the first time. The g-factor of 28P (Iπ =3+, T1/2=270.3 ms) was measured by means of β-NMR technique combined with the new polarization technique for charge exchange reaction product in the intermediate energy heavy ion collisions. The obtained g-factor of g=0.1028(27) is very much quenched from the Schmidt value, but is well reproduced by the shell model (+0.102). In connection with the magnetic moment of the mirror partner and the β-ray transition probability, the orbital angular momenta and intrinsic spins of protons and neutrons have been determined as lp =0.43(29), ln =1.85(29), Sp)=0.28(4), and Sn =0.44(4). Nuclear structure of proton-rich unstable nucleus 28P has been studied by measuring its g-factor for the first time. The g-factor of 28P (Iπ = 3 +, T1 / 2 = 270.3 ms) was measured by means of β-NMR technique combined with the new polarization technique for charge exchange reaction product in the intermediate energy heavy ion collisions. The obtained g-factor of g = 0.1028 (27) is very much quenched from the Schmidt value, but is well reproduced by the shell model ( +0.102). In connection with the magnetic moment of the mirror partner and the β-ray transition probability, the orbital angular momenta and the intrinsic spins of protons and neutrons have been determined as lp = 0.43 (29), ln = 1.85 (29) , Sp) = 0.28 (4), and Sn = 0.44 (4).