A wearable patch-type automatic defibrillator attachable to a region of a patient near the patient's heart includes a battery which stores electrical energy for defibrillation, a controller which controls the battery, electrocardiogram (ECG) electrodes, and defibrillation electrodes. The controller analyzes ECG signals of the patient received through the ECG electrodes, and automatically provides the patient with the electrical energy stored in the battery through the defibrillation electrodes when defibrillation is needed according to a result of the analysis.