Fourier transform method was used in the crack detector for the first time in the world. It detects cracked eggs by analyzing tones and acoustics of sound when the eggs are tapped. Tappers tap each egg 16 times from different directions continuously, and detect cracked eggs by analyzing its sound. While the detection rate by image-sensing is about 60%, the detection rate dramatically improved to 95% by this technology, as an invisible crack can be detected by its sound. In spite of its large size and thick eggshell, the crack detector can detect cracks on duck eggs with the same accuracy as on chicken eggs. It removes cracked eggs and assists an essential process of producing century eggs.