A fuel gas injection apparatus includes a chamber, a heat exchanger, a supply manifold, injectors, and a mount body. The chamber is in communication with a fuel gas tank, and the heat exchanger is in communication with the chamber. The supply manifold is in communication with the heat exchanger and has a plurality of branched flow channels for flowing a fuel gas. The plurality of injectors detachably communicate with the branched flow channels of the supply manifold. The mount body is in communication with the plurality of injectors and guides the fuel gas injected from plurality of injectors to a fuel cell stack. The chamber and the heat exchanger are attached to the mount body.