To provide a boiler in which a heat generation body is provided within a container, which is filled with hydrogen-based gas, and which can more effectively use the hydrogen-based gas.SOLUTION: A boiler includes a heat transfer pipe, a heat generation body, and a container within which the heat transfer pipe and the heat generation body are provided. The boiler is configured to heat the heat transfer pipe by using heat generated from the heat generation body in the state in which the inside of the container is filled with the hydrogen-based gas. The boiler includes a feed-out part which supplies the hydrogen-based gas with heat acquired from the heat generation body to a fuel pole of the fuel cell, and a feed-in part which supplies the hydrogen-based gas discharged from the fuel pole of the fuel cell into the container.SELECTED DRAWING: Figure 1