Provided is an ampoule-type reserve battery including: an ampoule casing having an accommodation part formed therein; an electrolyte accommodated in a lower portion of the accommodation part; a leakage prevention liquid made of oil, which is phase-separated from the electrolyte without being mixed therewith so as to prevent the electrolyte from leaking through an upper portion of the accommodation part, and accommodated in the upper portion of the accommodation part; and a separation membrane mounted in the accommodation part and configured to separate the electrolyte from the leakage prevention liquid.