Abstract: Non-destructive testing system performs accurate testing as to whether lamination joining portion of different metal materials is in strong joining state by secure metal joining. The system sets a lamination joining portion of different metal materials of a work to a certain position and angle. Laser light in certain waveform is applied to lamination joining portion surface to capture images by infrared camera, and data processing device obtains infrared images. Based on infrared images, Fourier transform is performed on each pixel of infrared images, and phase image is created by console device. Based on created phase image, effectiveness/defectiveness of joining is determined. In this non-destructive testing, whether reflection by vertical wall in vicinity is significant is determined, based on intensity of infrared images obtained immediately after irradiation with laser and angle between laser light optical axis and testing part surface is finely adjusted to obtain infrared images with less noise.