The anode mode of a vacuum are in a cathodic are deposition apparatus was observed as a function of ambient gas pressure ranging from 0.01 to 300 Pa. The chamber (400 mm in diameter and 600 mm in length) made of stainless steel (SUS304) acted as the anode. The are was operated at a relatively low constant current of 50 A. The cathode materials used were Al, Ti, Fe, Ni, and Cu, and ambient gases were He, Ne, Ar, H-2, N-2, O-2, and CH4. The principal results are as follows. (1) As the pressure was increased, the anode mode changed from diffuse-are to footpoint to plane luminous to anode-spot mode. (2) The anode mode and resultant are voltage increase were strongly dependent on gas species, and weakly on the cathode material. (3) Comparing diatomic and polyatomic(H-2, N-2, O-2, and CH4) with mono-atomic molecule gases (He, Ne, and Ar), the onset pressure of the anode mode transition in the former was lower, the are Voltage higher, and the footpoints more numerous, smaller, and clearer. Both-the dependence of the ambient pressure and the influence of the cathode materials and gas species on the anode mode changes were explained by the ion deficiency theory.