An ultrasonic inspection system includes an ultrasonic sensor and a control device. The ultrasonic sensor has a piezoelectric element that transmits and receives ultrasonic waves and plate portions and that are arranged so as to contact an upper surface of the piezoelectric element and have different thicknesses. The control device acquires a propagation time of a reflected wave reflected on an upper surface of the plate portion, calculates a sound velocity of the plate portion using the propagation time of the reflected wave and a thickness of the plate portion, and corrects a sound velocity of a pipe and acquires a sound velocity of the plate portion based on the calculated sound velocity. In addition, the control device acquires a propagation time of a reflected wave reflected on an upper surface of the plate portion, and calibrates a time axis based on the propagation time of the reflected wave, a thickness of the plate portion, and the sound velocity of the plate portion.