Atomic configuration at the equilibrium state, magnetic property and electronic state of CoVMnAl quaternary Heusler alloy were investigated by neutron diffraction, magnetic measurements, and first-principles calculations. Saturation magnetization measured at 5 K was quite small of 0.04 μ_B/f.u. for the specimen annealed at 873 K, and close to the expected value from the Slater-Pauling rule as predicted by Galanakis et al. (1983) [1]. Because the intensities of the superlattice diffractions of 111 and 200 were strong in the neutron diffraction, the atomic configuration of the CoVMnAl could be accurately determined. The best fitting was obtained as the L2_1b-type structure, in which the Co and Mn atoms randomly occupied the 8c site in the Wyckoff position in the space group number of 225. A small ferromagnetism was occurred in the specimen which was obtained by quenching at temperature above the order-disorder phase transition. The specimen exhibited a B2-like atomic configuration, where V and Al were partially distributed. Although the total energy in the LiMgPdSn-type ordered structure was 56 meV/f.u. lower than that in the L2_1b-type structure, the difference was small as the L2_1b-type structure would be obtainable in a finite temperature.