An apparatus for measuring ionizing radiation includes a detector having a cathode, an anode, a counting gas between the cathode and the anode for generating gas ionization by ionizing radiation, a voltage source for applying a voltage between the cathode and the anode, and a current measuring device for measuring a detector current between the cathode and the anode. The detector current is generated in the counting gas by the ionizing radiation. The apparatus further includes a setting device, wherein the setting device is configured for independently setting the apparatus into different operating modes depending on the measured detector current, and/or wherein the setting device is configured for independently setting the apparatus into different measurement ranges depending on the measured detector current.