Measurement principles of the ear sensor. The ear sensor is used for the measurement of “deep mouth breathing” and “nods.” An optical sensor and weight are attached to the ear sensor. The optical sensor has one infrared LED and one phototransistor embedded, infrared light is irradiated on to the epidermis of the ear canal, and as the inverted light is received by the phototransistor, it is able to measure movements in the ear canal and shaking of the ear sensor. The opening and closing operation of the mouth when humans breathe through the mouth is achieved through the expansion and contraction of the temporalis muscle. As there is a deformation in the shape of the adjacent ear canal due to the expansion and contraction of the temporalis muscle, this change can be measured optically and noninvasively using the ear sensor, to detect mouth breathing. Additionally, when the subject nods, the ear sensor to which the weight is attached shakes. As there is a change in the ear sensor measured values in accordance with this shaking, it can detect the nods of the subject.