Rotary transformer for rotary ultrasonic flaw detection device and rotary ultrasonic flaw detection device using same

This rotary transformer (5) for a rotary ultrasonic flaw detection device is provided with a flat plate-shaped stator (51) on one surface side of which coils are disposed, and a flat plate-shaped rotor (52) on one surface side of which coils are disposed, the respective coil disposition surface sides of the stator and the rotor are disposed to face each other, and signal transmission in the frequency band of 1-10 MHz is performed between the coils facing each other. The stator is provided with a substrate (512) on which a plurality of one-turn coils (511) are concentrically formed, and a holding member (513) for holding the substrate, and the rotor is provided with a substrate (522) on which the same number of one-turn coils (521) as the one-turn coils formed on the stator are concentrically formed, and a holding member (523) for holding the substrate. Air or a material that is an insulator and has a relative permeability approximately equal to 1 (M) lies between the substrate and the holding member which the