A test device for testing concentricity between first and second holes in parallel plates includes a positioning pole and a test pole. The positioning pole includes a head segment having a tapered positioning portion. The positioning pole axially defines a through hole. The test pole is telescopically received in the through hole of the positioning pole. The test pole includes a test head with a diameter slightly less than a diameter of the second hole. The positioning portion of the positioning pole extends into the first hole with the conic section of the positioning portion abutting against an inner wall bounding the first hole. The test head of the test pole faces the second plate and approaches and confirms the concentricity of the hole in the second plate by sliding the test pole relative to the positioning pole.