A hydrogen-generating device is provided, which includes a reaction tank, a first cap, a second cap and a first guiding-pipe. The reaction tank has an accommodation space for accommodating a solid reactant. The first cap covers the accommodation space, wherein the first cap has a plurality of first open-holes. The second cap is disposed on the first cap and has a second open-hole, wherein the first cap and the second cap form a chamber therebetween. The first guiding-pipe passes through the first cap and the second cap to extend to the accommodation space, wherein the first open-holes surround the first guiding-pipe. A liquid reactant is for passing through the first guiding-pipe to arrive in the accommodation space and reacts with the solid reactant to generate a hydrogen. The hydrogen passes through the first open-holes to arrive at the chamber and then is expelled from the second open-hole.