A system for producing a sound having a certain frequency range to maintain laying hens in stable and comfortable conditions. includes a basic wave generator for generating a pair of first basic waves having the same phase and a pair of second basic waves having opposite phases, a relaxation wave generator for generating a pair of relaxation waves by combining the pair of first basic waves and the pair of second basic waves with time, a modulator for generating a pair of relaxation sounds by modulating the pair of relaxation waves with a sound wave having an audible frequency, and an audio output unit composed of two left and right parts such that stereo sound is outputted, for receiving the pair of relaxation sounds and outputting the pair of relaxation sounds to the left and right parts, respectively.