PROBLEM TO BE SOLVED: To obtain an electron donor supply device which can eliminate a waste consumption of an electron donor substance due to leakage in a distribution process, can supply the electron donor substance to microorganisms when being in contact with water, and can control the amount of supplied electron donor substance without using a pump and a controller.SOLUTION: The electron donor supply device includes the electron donor substance 3 serving as an energy source to the microorganisms, a container 4 having a sealed structure which has a non-porous film 2a having a hydrophobic property on at least a part thereof, and a hydrophilic non-porous film 2b. The electron donor substance 3 fills the container 4, and a hydrophobic non-porous film 2a portion on the outside surface of the container 4 is covered with the hydrophilic non-porous film 2b. Instead of using the hydrophobic non-porous film 2a and the hydrophilic non-porous film 2b together, a polylactic acid film may be used.
