A liquid filling aid that is placed on a plate-shaped member and defines a reaction chamber to be filled with a liquid, the aid includes a main body, a storage section that is formed in the main body and stores the liquid, a reaction section that is a recess formed at a bottom of the main body, a communication aperture for fluid communication between the storage section and the reaction section, and an air vent for communication between the reaction section and outside air, wherein the reaction section and an upper surface of the plate-shaped member define the reaction chamber and a liquid filling method including a step of placing the liquid filling aid on the plate-shaped member, and a step of discharging the liquid in an amount equal to or larger than the volume of the reaction chamber for supply to the storage section.
