A hydrogen gas generator comprises: an electrolyzer (2) configured to include a housing (20), a first chamber (21), a second chamber (22), a membrane (25), and a pair of electrode plates (23, 24)； a tank (6) configured to store water to be electrolyzed (W)； an electric power source (3) configured to apply a DC voltage to the pair of electrode plates； a diluter (4) configured to introduce a diluent gas into the first chamber or the second chamber in which the electrode plate to be a cathode is provided, the diluent gas diluting hydrogen gas generated； an electric quantity detector (51) configured to detect an electric quantity given to the electrode plate to be the cathode； a flow rate detector (52) configured to detect a flow rate of the diluent gas from the diluter； a calculator (5) configured to calculate a concentration of the diluted hydrogen gas on the basis of the electric quantity detected by the electric quantity detector and the flow rate detected by the flow rate detector； and an indicator (54) configured to present the concentration of hydrogen gas calculated by the calculator.包括：電解槽2，包含框體20、第一室21、第二室22、隔膜及25一對電極板23、24；儲槽6，貯留被電解水W；電源3，將直流電壓施加於上述一對電極板；稀釋器4，將稀釋已生成的氫氣的稀釋氣體導入設有成為陰極的電極板之上述第一室或上述第二室；電量檢測器51，檢測被賦予至成為上述陰極的電極板的電量；流量檢測器52，檢測上述稀釋器造成的稀釋氣體的流量；演算器5，根據藉由上述電量檢測器而檢測的電量及藉由上述流量檢測器而檢測的流量，演算上述被稀釋的氫氣的濃度；以及提示器54，提示由上述演算器演算之氫氣的濃度。
