Abstract: The invention relates to an apparatus for detecting an electromagnetic pulse having a given origin, more particularly due to a nuclear explosion. This apparatus comprises means for sensing the electrical component of an electromagnetic pulse, means for differentiating a signal supplied by the sensing means from an electromagnetic pulse of a given origin from another pulse and means for taking note of the result of the detection. The differentiation means advantageously comprise means for detecting the passage of the signal supplied by the sensing means at a value exceeding a threshold value, a time counter started by the detection means during the detection of said passage, means for integrating the signal supplied by the sensing means and means for comparing the value of the integrated signal up to time t.sub.1 following the starting of the sensor with a reference value.