We investigate the interband coupling induced odd-frequency pairing state by solving the microscopic Ginzburg-Landau model for the two band superconductor magnesium diboride (MgB₂). It is found that the interband coupling can induce a new domain structure and a heliacal spontaneous magnetic vortex-antivortex pair around the cyclical domain wall, which breaks down spin-rotational symmetry and supports a time-reversal violating bound state, allowing the coexistence of spin-singlet and spin-triplet state close to the spontaneous vortex core. The odd-frequency spin-triplet even parity pairing state occurs since a successive operation in the orbital parity (P) and the time-reversal (T) obeys PT = + 1(–1) for spin-singlet (spin-triplet) pairing amplitude. A general phase diagram is presented.