An ionizing radiation detection apparatus of the present disclosure includes a first drift electrode disposed inside a chamber and a first detection unit disposed inside the chamber so as to oppose the first drift electrode, wherein the first detection unit is configured to detect a first ionization electron produced through Compton scattering caused by an incident γ-ray inside the scattering gas, and a second drift electrode configured to emit a reference X-ray upon being excited by the incident γ-ray with a second detection unit disposed so as to oppose the second drift electrode and configured to detect a second ionization electron produced as the reference X-ray is photoelectrically absorbed by the scattering gas, and a control unit configured to compensate for a change in an amplification factor of a signal output from each of the first detection unit and the second detection unit.