An electromagnetic radiation measuring device includes a test antenna module and a main processor electrically connected to the test antenna module. The test antenna module includes a plurality of pre-test antennas and at least one final test antenna, which have predetermined polarities and are positioned at predetermined heights, respectively. The pre-test antennas and the final test antenna respectively receive wireless signals sent from an electronic device. The main processor measures and records a frequency of the strongest wireless signal received by selected ones of the pre-test antennas that have the same polarity, and further determines whether power of wireless signals at the recorded frequency received by the final test antenna polarized to have the same polarity as that of the selected ones of the pre-test antennas exceeds a predetermined acceptable range.