PROBLEM TO BE SOLVED: To provide a system that can accurately measure a wall thickness of a steel pipe even if the steel pipe has a small diameter, and can be applied for the actual operation related to manufacturing of the steel pipe.;SOLUTION: A steel pipe wall thickness measuring apparatus uses an irradiation optical system 120 including a galvanomirror 121 to irradiate, with an ultrasonic wave generation laser beam 111, a plurality of measurement points provided over the whole circumference of an external surface 201G of a steel pipe 200 in a sequentially switching manner, and generates an ultrasonic wave propagating in a wall thickness direction of the steel pipe 200 for each of the plurality of measurement points. A plurality of transmitting/receiving units 142 that are provided corresponding to each of the plurality of measurement points irradiated with the ultrasonic wave generation laser beam 111 and transmit and receive an ultrasonic wave detection laser beam 131 at each of the plurality of measurement points, are sequentially switched according to sequentially switching irradiation of the ultrasonic wave generation laser beam 111 by the irradiation optical system 120 using an optical switch 141.;COPYRIGHT: (C)2015,JPO&INPIT
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