This hydrogen-oxygen reaction device includes a reaction vessel including a reaction region filled with a reaction catalyst which promotes a reaction between hydrogen and oxygen, an introduction portion which introduces an hydrogen-oxygen mixed gas having hydrogen or oxygen as a main component into the reaction vessel, a water vapor pipe of which one end portion is inserted into the reaction vessel and which includes a region in contact with the reaction region with at least a part of the region in contact with the reaction region being formed of a water vapor permeable membrane, a discharge portion through which a gas in the reaction vessel is discharged to an outside, and a cooling portion which cools the water vapor pipe outside the reaction vessel.