Particularly, there is provided a liquid detection sensor in which a liquid contact area is formed integrally with a separator, and that improves detection accuracy with a small number of parts. A liquid detection sensor (1) according to the present invention includes a metal-air battery (2) formed by laminating a negative electrode sheet (3), a positive electrode sheet (5) and a separator (4) interposed between the negative electrode sheet (3) and the positive electrode sheet (5), and the separator (4) is formed wider than an area in which the positive electrode sheet (5) and the negative electrode sheet (3) overlap with the separator (4) interposed therebetween, and includes a liquid contact area (4′) exposed from at least one of the positive electrode sheet and the negative electrode sheet.