PURPOSE: To obtain a apparatus for testing deteriorated oil resistance of a rubber meterial by pressurized oxygen and a testing method using the apparatus, which can reproduce the phenomenon of deterioration of the rubber material from a view point in conformity with practical conditions and can evaluate it precisely and efficiently.

CONSTITUTION: In a testing apparatus, an opening 22 for fixing a test piece is provided in a part of a cylinder 10 for testing which is formed of a pressure- proof vessel 11 in which oil is head and of a jacket 15 covering the pressureproof vessel 11 with a gap 13 provided between. Moreover, an oxygen supply pipe 17 is fitted to the pressure-proof vessel 11 and pipings 23 and 25 for circulating a medium 34 for adjustment of temperature through the gap 12 are fitted thereto. As for a testing method, a test piece 19 is fixed to the opening part 22 for fixing the test piece so that only one side of the piece is in contact with oil, the oil held inside the cylinder 10 is deteriorated forcedly and the effect of the deteriorated oil on the test piece 19 and others are checked up.