To provide ultrasonic rail head transverse cracking flaw device and method that can securely detect transverse cracking in a rail head.

Between the ultrasonic transmission position of a transmission probe 14 being arranged at the side RS1 of a rail head, and the ultrasonic reception position of a reception probe 15 being arranged at the side RS2 of the rail head, a first distance L1 is arranged in the longitudinal direction of a rail R, and at the same time a second one L2 is arranged in the vertical direction of the section of the rail R.