The present invention provides a corrosion loss measuring apparatus which enables to quantitatively determine corrosion loss characteristics of ceramic materials and heat-resistant metallic materials, which is excellent in terms of safety, cost, and operation easiness, and whose size can be reduced. The invention also provides a method for measuring corrosion loss by use of the apparatus. The corrosion loss measuring apparatus which, in use, allows an atmosphere gas to be continuously fed into a test-piece-placing section for accommodating a material test piece, the atmosphere gas having a predetermined composition and having been heated to a predetermined temperature, wherein the apparatus includes a gas-heating section and a test-piece-placing section, the gas-heating section and the test-piece-placing section are included a one-piece ceramic-made tube for use in a heating furnace, and the cross-sectional area of the gas-heating section through which the gas flows is larger than that of the test-piece-placing section.