PURPOSE: To obtain an inspecting apparatus for a rectangular steel material which can continuously inspect the defects in the entire surface of a rectangular steel material having the rectangular shape.

CONSTITUTION: A rectangular-steel-material inspecting apparatus for defecting the defect of material, whose cross section is an approximately rectangular paralleopiped, is provided with a penetrating-type eddy-current flaw detecting device 7 and an ultrasonic-wave flaw detecting device on the same conveying line. The penetrating-type eddy-current-flaw detecting device 7 is provided on the conveying line in the longitudinal direction of the rectangular steel material so that the rectangular steel material penetrates through a flaw detecting coil 5. The ultrasonic wave flaw detecting device has an ultrasonic-wave probe, which emits the ultrasonic wave obliquely into the surface of the rectangular steel material and detects the flaw.