A device for the nondestructive material testing of an at least sectionally solid test subject by applying ultrasonic waves to the test subject and detecting the ultrasonic waves reflected inside the test subject is provided The device includes at least one testing head for transmitting the ultrasonic waves and for detecting the ultrasonic waves reflected from the test subject, at least one mobile carriage, on which the testing head is attached, and an elongate rail for guiding the carriage, which is adapted to the structure of the surface of the test subject. To this end, the carriage may be moved along the rail.