PURPOSE:To achieve a higher reliability by cutting a discshaped product containing carbon diametrically to take a doughnut-shaped sample, which is heated ra pidly with a coil of a high frequency induction heater provided along the inner surface thereof. CONSTITUTION:A coil 2 of a high frequency induction heater is arranged along the inner surface of a doughnut-shaped sample 1 taken from a product containing carbon to evaluate the heat impact resistance. Then, under such a condition, a high frequency is applied to the coil to cause a secondary induction current in the sample 1 thereby heating the sample 1 rapidly from the inner surface thereof 1. Consequently, a temperature gradient is generated in the sample and causes a large tensile stress to work on the circumference of the sample 1 due to the resulting thermal expansion, eventually cracking or destroying the sample 1. Then, the output value to be applied to the high frequency inducion heater to define the output value when causing a cracking as the coefficient of heat impact resistance of the sample. Thus, a high reliability with an excellent reproducibility can be obtained.
