Automatic external defibrillator and method for notifying abnormality of automatic external defibrillator

An AED (1) has a detector (10) and a notifier. The notifier has a display unit (40) and a sound generator (50). The display unit (40) alternately executes the first mode and the second mode one or more times, respectively. In the first mode, the display unit (40) causes the at least one light source (42) to emit light of a first intensity. In the second mode, the display unit (40) causes the light source (42) to emit light of a second intensity lower in power consumption than the first intensity or causes the light source (42) not to emit light. The sound generator (50) alternately executes the third mode and the fourth mode one or more times, respectively. In the third mode, the sound generator (50) generates a warning tone of a third intensity. In the fourth mode, the sound generator (50) generates or does not generate a prompt tone of a fourth intensity with lower power consumption than the third intensity. At least half of each period of the first mode overlaps in time with a corresponding period of the f