A detecting apparatus for use in specifying regions having different impurity concentrations in an ingot includes an ingot holding unit having a holding surface for holding the ingot thereon, an excitation light source for applying excitation light having a predetermined wavelength to a face side of the ingot held on the holding surface, and a photodetector for detecting fluorescence emitted from the ingot upon exposure to the excitation light and generating an electric signal representing a number of photons of only light whose wavelength is in an infrared radiation range, of the detected fluorescence.