A hot flaw detector is equipped with a sensor holding member that has a circular opening through which the material to be inspected will pass and that holds a flaw detecting sensor. Provision is made of an annular cooling liquid injection port that is open at an end of the sensor holding member adjacent to the inner peripheral wall of the circular opening, and provision is further made of an annular cooling liquid introduction port that is open at the other end of the sensor holding member adjacent to the inner peripheral wall of the circular opening. The cooling liquid is injected from the annular cooling liquid injection port, and forms a liquid film along the inner peripheral wall of the circular opening, and is recovered through the annular cooling liquid introduction port. The inner peripheral wall of the sensor holding member is effectively cooled by the liquid film which drips little onto the material to be inspected.