Disclosed are a testing apparatus for and a method of measuring thermal stresses of concrete structures. Overcoming the limitations that conventional analytical access techniques have, the apparatus opens a new way to conveniently measure the thermal stress attributable to the heat of hydration generated in concrete structures indoors. Using a material different in coefficient of thermal expansion from concrete, the apparatus can directly measure the change in thermal stress of the concrete which is subjected to internal and/or external confinement. By using various materials, the thermal stress which varies depending on the confinement extent can be inferred. Additionally, an accurate prediction of the thermal stresses generated actually in concrete can be obtained, reflecting unclear physical properties of early-age concrete.