To provide a stimulus-response evaluation device constituted so as to allow the living body of a person, an animal or the like to be inconscious of the measurement of external stimulation when the response of the living body to external stimulation is measured by converting the breathing action of the living body to an electric signal.

A hermetically sealed pneumatic sound sensor is brought into close contact with the living body or incorporated in each of the legs of a bed or chair to which the weight of the living body is applied to measure the breathing action of the living body in such a state that the living body is inconscious of measurement. The measured result is converted to an electric signal and analyzed to decide the mental state of the living body or the environment in which the living body is placed. Further, the electric signal is used for adjusting an environment adjusting device.