To provide a method and device for diagnosing the existence of cracks which can be used to be incorporated in a tile inspection device of a mass production manufacturing process by providing a quantitative, accurate and economical method and device for diagnosing the existence of the cracks of a ceramic, plastic or metal product for instance, a tile by an acoustic signal generated by a blow.

The diagnosing device comprises converting the acoustic signal from the tile generated during the blow as a means for diagnosing the existence of the cracks of the tile, analyzing a frequency by high speed Fourier transform or the like, extracting the maximum value of a prescribed frequency region, calculating a difference between the maximum value and the reference maximum value being the acoustic signal of the normal product tile, and judging whether the difference is the prescribed value or more. The tile is mounted on a support body of a cushion material, hitted from the upper side or the lower side of the tile by an elastic sphere to generate hitting sound.