PURPOSE:To certainly evaluate residual life in a non-destructive manner within a short time, by measuring the diameter and surface density of minute voids generated in the crystal grain boundary of heat resistant steel and comparing the same with a residual life evaluation reference line chart preliminarily calculated. CONSTITUTION:The minute voids on the surface of heat resistant steel having the same material quality as a member to be inspected and used under various conditions are observed by a scanning type electronic microscope to measure the diameter and surface density thereof and line density being a product of both of them is calculated to form a residual life evaluation reference line chart. Next, the diameter and surface density of minute voids of heat resistant steel having been used for a long time are measured by a similar method. Because the length of the minute voids per a unit time being the product of the diameter and surface density is correlative to a creep breaking life consumption rate, a residual life estimation value is obtained from at least one of the reference line chart and measured physical values. Therefore, residual life can be certainly evaluated in a non-destructive manner within a short time.