A hydrogen generating unit for producing hydrogen water, comprising: a housing; and a cap comprising a circular flange which has a passing hole formed at a center of the cap, and a cylindrical joint pipe which protrudes downward from the flange, and screw threads which are formed on an outer surface of the joint pipe, wherein the housing includes a head at the upper side thereof, and a connecting pipe that protrudes downward from the head, a catching projection is formed between an insertion hole in the head and the connecting pipe, an upper electrode and a lower electrode are coupled between a lower portion of the joint pipe of the cap and the catching projection of the head when the joint pipe of the cap is inserted into the insertion hole of the head, and a diaphragm is interposed between the upper electrode and the lower electrode, wherein recessed surfaces (51, 52), which are recessed downward from an upper surface of the head, are formed in an outer circumferential surface of the head, through holes (53, 54), which penetrate the outer circumferential surface of the head from a space of the insertion hole in the head, are formed at lower sides of the recessed surfaces (51, 52), respectively, and an electrode terminal of the upper electrode and an electrode terminal of the lower electrode are exposed to the outside of the head through the through holes (53, 54) of the head, respectively, wherein the upper electrode and the lower electrode have flat circular plates (23; 26), respectively, and a plurality of pores (24, 27) is formed at central portions of the plates (23, 26) at small intervals, respectively. a housing; and a cap comprising a circular flange which has a passing hole formed at a center of the cap, and a cylindrical joint pipe which protrudes downward from the flange, and screw threads which are formed on an outer surface of the joint pipe, wherein the housing includes a head at the upper side thereof, and a connecting pipe that protrudes downward from the head, a catching projection is formed between an insertion hole in the head and the connecting pipe, an upper electrode and a lower electrode are coupled between a lower portion of the joint pipe of the cap and the catching projection of the head when the joint pipe of the cap is inserted into the insertion hole of the head, and a diaphragm is interposed between the upper electrode and the lower electrode, wherein recessed surfaces (51, 52), which are recessed downward from an upper surface of the head, are formed in an outer circumferential surface of the head, through holes (53, 54), which penetrate the outer circumferential surface of the head from a space of the insertion hole in the head, are formed at lower sides of the recessed surfaces (51, 52), respectively, and an electrode terminal of the upper electrode and an electrode terminal of the lower electrode are exposed to the outside of the head through the through holes (53, 54) of the head, respectively, wherein the upper electrode and the lower electrode have flat circular plates (23; 26), respectively, and a plurality of pores (24, 27) is formed at central portions of the plates (23, 26) at small intervals, respectively.