A hair sensor, which can suppress mixing of external noise to a minimal level when a sliding sound of hair is detected, amplified, and output as an audio output in order to estimate surface characteristics and the degree of hair damage, and which can be easily used, is provided. The hair sensor for detecting the sliding sound of the hair in order to estimate hair characteristics includes a sliding element capable of sliding on the hair and a housing which includes a microphone provided therein. The sliding element is erected on a diaphragm. The sliding element and the diaphragm are arranged to allow the sliding sound caused by the sliding element to be transmitted through the diaphragm to the microphone and to attenuate vibration transmitted from outside of the diaphragm to the microphone. The surface of the sliding element is preferably treated to have a roughened surface in order to improve slidability thereof during measurement and measurement accuracy.