A method was investigated for nondestructive evaluation of 2-D crack or slit depth by measurement of temperature difference between two points on the material surface in non contact. In the first, experiment was performed on the specimens of 304 stainless steel with a slit. Local temperature field around the crack or slit was formed by heating small area near the crack or slit with Nd : YAG laser beam, and temperature at a point was measured by infrared thermography. The slit depth was evaluated exactly by comparing experimental results with numerical analysis of non-steady heat conduction problem. Next similar experiment was carried out to evaluate the fatigue crack depth. However it was difficult to evaluate crack depth. because formed temperature field hardly changed either existence of the crack or not. So the effect of crack opening displacement on the temperature field was examined. It is shown that evaluating crack depth is possible by the present method, provided that load is applied to open the crack.