A combustion device for hydrogen-rich gas is provided. Before entering a chamber, fuel and air are non-premixed for avoiding flushback. A vortex generator and a fuel sprayer are combined to mix fuel and air for enhancing burning effect. Vortex flame is generated with stabilizing aerodynamics of flow provided through vortex breakdown. A flameholder is formed downstream an injector to maintain stable combustion. Cooling air is introduced from a sheath to cool down a high-temperature gas, which leaves the combustion chamber and drives a turbine for turning a power generator. Thus, the present invention effectively mixes fuel and air, avoids flushback and prevents combustor damage.