Abstract: An ultrasonic wave probe comprises an ultrasonic wave transmitting vibrator and a pair of ultrasonic wave receiving vibrators in order to measure blood flow velocity. The receiving vibrators are adapted to receive reflected waves of an ultrasonic wave which is emitted from the transmitting vibrator and reflected from a measured point at different receiving angles and the difference between the receiving angles of the receiving vibrators is always kept to a given value. The ultrasonic wave probe further includes an ultrasonic wave transmitting and receiving vibrator for measuring blood vessel diameter deviation at the same time as the measurement of the blood flow velocity.