A system for producing hydrogen, comprising: a dehydrogenation reaction unit for producing hydrogen from an organic hydride by a dehydrogenation reaction in presence of a dehydrogenation catalyst; a first power generation unit for generating electric power from energy of combustion gas produced by combustion of fuel; a waste heat recovery unit for receiving heat from exhaust gas expelled from the first power generation unit; a heat exchanger provided in the waste heat recovery unit for exchanging heat between the exhaust gas and a heat medium; and a circulation line (L1-L3) for introducing the heat medium heated in the heat exchanger to the dehydrogenation reaction unit in liquid form, and returning the heat medium expelled from the dehydrogenation reaction unit to the heat exchanger; wherein the heat exchanger is configured to heat the heat medium by the heat exchange between the exhaust gas and the heat medium such that the heat medium is introduced into the dehydrogenation reaction unit at an introduction temperature ranging between 352 °C and 392 °C; and wherein the system further comprises: a temperature detector provided in a part of the circulation line to detect a temperature of the heat medium that is expelled from the dehydrogenation reaction unit; and a flow rate regulator valve provided in a part of the circulation line to adjust a flow rate of the heat medium that is introduced into the dehydrogenation reaction unit according to the temperature detected by the temperature detector such that the heat medium is expelled from the dehydrogenation reaction unit at an expulsion temperature ranging between 337 °C and 367 °C, and a difference between the introduction temperature and the expulsion temperature ranges between 10 °C and 50 °C. a dehydrogenation reaction unit for producing hydrogen from an organic hydride by a dehydrogenation reaction in presence of a dehydrogenation catalyst; a first power generation unit for generating electric power from energy of combustion gas produced by combustion of fuel; a waste heat recovery unit for receiving heat from exhaust gas expelled from the first power generation unit; a heat exchanger provided in the waste heat recovery unit for exchanging heat between the exhaust gas and a heat medium; and a circulation line (L1-L3) for introducing the heat medium heated in the heat exchanger to the dehydrogenation reaction unit in liquid form, and returning the heat medium expelled from the dehydrogenation reaction unit to the heat exchanger; wherein the heat exchanger is configured to heat the heat medium by the heat exchange between the exhaust gas and the heat medium such that the heat medium is introduced into the dehydrogenation reaction unit at an introduction temperature ranging between 352 °C and 392 °C; and wherein the system further comprises: a temperature detector provided in a part of the circulation line to detect a temperature of the heat medium that is expelled from the dehydrogenation reaction unit; and a flow rate regulator valve provided in a part of the circulation line to adjust a flow rate of the heat medium that is introduced into the dehydrogenation reaction unit according to the temperature detected by the temperature detector such that the heat medium is expelled from the dehydrogenation reaction unit at an expulsion temperature ranging between 337 °C and 367 °C, and a difference between the introduction temperature and the expulsion temperature ranges between 10 °C and 50 °C. a temperature detector provided in a part of the circulation line to detect a temperature of the heat medium that is expelled from the dehydrogenation reaction unit; and a flow rate regulator valve provided in a part of the circulation line to adjust a flow rate of the heat medium that is introduced into the dehydrogenation reaction unit according to the temperature detected by the temperature detector such that the heat medium is expelled from the dehydrogenation reaction unit at an expulsion temperature ranging between 337 °C and 367 °C, and a difference between the introduction temperature and the expulsion temperature ranges between 10 °C and 50 °C.