The ultrasonic probe of the ultrasonic inspection apparatus, which is pushed onto the outer surface of the reactor pressure vessel, transmits and receives an ultrasonic wave to and from a penetration having a welded portion while changing an incident angle of the ultrasonic wave. Based on a result of reception of an echo obtained by the reflection of the ultrasonic wave on the inner surface of the penetration, an inclination angle of the penetration relative to a wall surface of the reactor pressure vessel is measured. A circumferential direction position of the penetration, which corresponds to the inclination angle, is calculated based on the relationship of an inclination angle and a circumferential direction position, which have been calculated in advance. Then, the circumferential direction position can be obtained as information on the inspection position.