[Technical problem] Circulatory sound regulation that changes environmental sound into input sound, converted sound with arbitrarily regulatory frequency component, arbitrarily regulatory amplitude or both of them, output sound, another input sound synthesized with this output sound and an environmental sound, and another converted sound made from this input sound. [Solution] Apparatus comprising: input means that receives environmental sound from arbitrary environment as an input sound; conversion means that converts the input sound into a converted sound that contains arbitrarily regulatory frequency component including frequency component that approximates to principle oscillator, arbitrarily regulatory amplitude or both; and output means that transmits the converted sound to environment as an output sound; whereby the input means receives synthetic sound synthesized with the output sound and environmental sound as an input sound again, and the conversion means converts this input sound further into another converted sound.