An ultrasonic probe includes an optical resonating waveguide configured to receive an echo ultrasound signal; a calculator configured to calculate an acoustic pressure of the echo ultrasound signal, based on a change in wavelength of an optical signal traveling within the optical resonating waveguide, the change occurring in response to the optical resonating waveguide receiving the echo ultrasound signal; and a converter configured to convert the echo ultrasound signal to an electric signal based on the acoustic pressure of the echo ultrasound signal.