Abstract: The present invention is: a blood flow sensor that sandwiches a longitudinal-direction section of a blood vessel of a subject, from the outer circumference of such section, to generate an electrical signal corresponding to the blood flow; and a blood flow measurement instrument that processes the electrical signal from the blood flow sensor and converts the signal to an electrical signal indicating blood flow. The blood flow sensor and the blood flow measurement instrument are provided with connectors so as to be mechanically and electrically separable from each other.