A flexible sheet-type leak sensor device according to the present invention comprises: a flexible base sheet made of a non-conductive fluorine-based synthetic resin comprising ethylene tetrafluoroethylene (ETFE); conductive lines formed on a surface of the base sheet so as to have a predetermined pattern and so as not to meet or cross each other, the conductive lines being formed by depositing on the base sheet surface a carbon black-containing, conductive fluorine-based synthetic resin comprising ethylene tetrafluoroethylene (ETFE); and a conductive material composed of pure carbon black, formed at the bottom of the conductive lines.