NOVELTY - The hydrogen generator (1) has a reactor (2) for generating hydrogen, storage chamber (8) existing in the reactor, fluid chamber, solution reservoir (4), fluid flow path, hydrogen exhaust passage (15), hydrogen exhaust passage (16) and control unit. The reactor and solution reservoir are communicated by fluid flow path.    USE - Generator is used for generating hydrogen (claimed) for fuel cell and hydrogen fueled engine.    ADVANTAGE - The hydrogen generator efficiently generates hydrogen, without providing drive source for movement of fluid.    DETAILED DESCRIPTION - The hydrogen generator (1) has a reactor (2) for generating hydrogen, storage chamber (8) existing in the reactor, fluid chamber, solution reservoir (14), fluid flow path, hydrogen exhaust passage (15), hydrogen exhaust passage (16) and control unit. A solid reaction material is accommodated in the storage chamber in the reactor. The fluid chamber varies volume of the storage chamber. A promoter aqueous solution which generates hydrogen by contacting with the solid reaction material is accommodated in the solution reservoir. The reactor and solution reservoir are communicated. The fluid flow path sends out hydrogen from the reactor to the reservoir. The flow path edge portion at the side of the solution reservoir contacts the promoter aqueous solution. The solution reservoir and fluid chamber are communicated by hydrogen flow path which sends out from the reservoir to the fluid chamber. The passage (15) discharges hydrogen to the reservoir. The passage (16) discharges hydrogen to the fluid chamber. The promoter aqueous solution is circulated in fluid flow path by pressure reduction in storage chamber to the fluid chamber by generation and discharge of hydrogen. The control unit circulates hydrogen in the fluid flow path and makes the reaction product to contact promoter aqueous solution while controlling circulation of hydrogen of hydrogen flow path, passage (15) and passage (16).    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic block diagram of the hydrogen generator.    Hydrogen generator (1)    Reactor (2)    Solution container (4)    Promoter aqueous solution (5)    Storage chamber (8)    Hydrogen exhaust passages (15,16)