An apparatus includes a thermal guide element to contact a specific site of a subject to apply a thermal stimulus from the thermal guide element to the specific site； an electrical thermal stimulus controller to raise a temperature of the thermal guide element； and a laser Doppler tissue blood flow meter attached to the subject. The electrical thermal stimulus controller raises a peak temperature of the thermal guide element to be 50±5° C. when the thermal guide element is brought into contact with the specific site to apply the thermal stimulus to the specific site, while measuring the rate of the blood flow by the laser Doppler tissue blood flow meter. The rate of the blood flow is increased in the subject by 30% or more as compared with the rate of the blood flow measured before the application of the thermal stimulus.
