To provide an automatic external defibrillator capable of quickly and appropriately discriminating a control/selection operation between an adult mode and a child mode and allowing the easy and simple operation without any erroneous operation.

This automatic external defibrillator is provided with an electric energy source 10, a pair of paddle electrodes 20, and a controller 30 setting a control program for selectively operating as the adult mode or the child mode and generating defibrillation electric shock suited to the use for the adult or the child. This defibrillator has selection switches 42 and 44 for setting the adult mode or the child mode, discharge buttons for applying the electric shock suited to the use for the adult or the child respectively, and a first opening/closing lid and a second opening/closing lid displayed with letters and graphics indicating the adult or the child on the surface and the back face of the outer case of the defibrillator, and is configured to actuate the mode selection switch in response to the opening operation of one opening/closing lid and operate a corresponding discharge button.