A hot flaw detector of the invention has a round opening through which a test material is passed and a sensor holding member for holding a flaw detection sensor. An annular coolant ejection port is disposed so as to open at a position adjacent to the inner peripheral wall of the round opening at one of the ends of the sensor holding member, and an annular coolant inlet is disposed so as to open at a position adjacent to the inner peripheral wall of the round opening at the other end of the sensor holding member. The coolant is ejected from the coolant ejection port and recovered into the coolant inlet while forming a liquid film along the inner peripheral wall of the round opening. The inner peripheral wall of the sensor holding member is cooled effectively by the liquid film and the chance of dropping and scattering of the coolant onto the test material is little.
