Spontaneous formation of coherent vector fields, which results from synchronization of longitudinal modes of orthogonally polarized transverse modes, has been observed in a laser-diode (LD)-pumped thin-slice c-cut Nd:GdVO(4) laser with reflective end faces operating under the multi-longitudinal mode oscillation condition. The suppression of antiphase dynamics inherent to multimode solid-state lasers as well as the enhanced self-mixing interference effect as compared with a linearly polarized multimode laser have been identified.