Abstract: An apnea preventing stimulation apparatus in which a conductive unit is attached to a mental region of a patient and electric pulses conduct from the conductive unit to the mental region of the patient to thereby apply stimulation thereto. The apparatus includes a stimulus generating means that outputs, across output terminals of the conductive unit, stimulation signals which alternately repeat, for a preset time, a conduction period during which electric pulse groups comprising plural electric pulses are generated and a pause period during which no electric pulse groups are generated. Hence, without monitoring a respiratory condition during sleep, the upper airway obstruction can be quickly prevented. Further, as the stimulation signals can be applied to the patient irrespective of presence or absence of respiration of the patient, the patient hardly awakes by sensing the stimulation signals.