An electrolytic apparatus comprising: an electrolyzer that includes an anode chamber accommodating an anode, a cathode chamber accommodating a cathode, and a diaphragm partitioning the anode chamber and the cathode chamber; a cathode side electrolyte discharge line connected to the cathode chamber to discharge a cathode side electrolyte containing hydrogen gas from the cathode chamber; a cathode side gas-liquid separating means connected to the cathode side electrolyte discharge line to separate the hydrogen gas from the cathode side electrolyte; a hydrogen gas discharge line connected to the cathode side gas-liquid separating means to discharge the hydrogen gas separated by the cathode side gas-liquid separating means from the cathode side gas-liquid separating means; and a gas compression means connected to the hydrogen gas discharge line, wherein the gas compression means includes a cathode side ejector connected to the hydrogen gas discharge line, a cathode side storage tank that stores the hydrogen gas and a cathode side circulation liquid flowing in the gas compression means, a cathode side fluid mixture feed pipe that connects the cathode side ejector and the cathode side storage tank to each other, and feeds a fluid mixture of the cathode side circulation liquid and the hydrogen gas from the cathode side ejector to the cathode side storage tank, a cathode side circulation pipe that connects the cathode side storage tank and the cathode side ejector to each other, and feeds the cathode side circulation liquid from the cathode side storage tank to the cathode side ejector, a cathode side circulation pump installed in the cathode side circulation pipe, a hydrogen gas discharge pipe connected to the cathode side storage tank to discharge the hydrogen gas from the cathode side storage tank, and a first valve provided in the hydrogen gas discharge pipe, the hydrogen gas is allowed to flow into the cathode side ejector from the hydrogen gas discharge line by circulating the cathode side circulation liquid from the cathode side storage tank to the cathode side ejector using the cathode side circulation pump, the cathode side fluid mixture feed pipe, and the cathode side circulation pipe, the hydrogen gas and the cathode side circulation liquid are mixed in the cathode side ejector, and an impurity in the hydrogen gas is transferred to the cathode side circulation liquid to remove the impurity from the hydrogen gas, and a pressure of the hydrogen gas stored in the cathode side storage tank is raised by controlling a flow rate of the cathode side circulation liquid circulated from the cathode side storage tank to the cathode side ejector and opening and closing of the first valve. an electrolyzer that includes an anode chamber accommodating an anode, a cathode chamber accommodating a cathode, and a diaphragm partitioning the anode chamber and the cathode chamber; a cathode side electrolyte discharge line connected to the cathode chamber to discharge a cathode side electrolyte containing hydrogen gas from the cathode chamber; a cathode side gas-liquid separating means connected to the cathode side electrolyte discharge line to separate the hydrogen gas from the cathode side electrolyte; a hydrogen gas discharge line connected to the cathode side gas-liquid separating means to discharge the hydrogen gas separated by the cathode side gas-liquid separating means from the cathode side gas-liquid separating means; and a gas compression means connected to the hydrogen gas discharge line, wherein the gas compression means includes a cathode side ejector connected to the hydrogen gas discharge line, a cathode side storage tank that stores the hydrogen gas and a cathode side circulation liquid flowing in the gas compression means, a cathode side fluid mixture feed pipe that connects the cathode side ejector and the cathode side storage tank to each other, and feeds a fluid mixture of the cathode side circulation liquid and the hydrogen gas from the cathode side ejector to the cathode side storage tank, a cathode side circulation pipe that connects the cathode side storage tank and the cathode side ejector to each other, and feeds the cathode side circulation liquid from the cathode side storage tank to the cathode side ejector, a cathode side circulation pump installed in the cathode side circulation pipe, a hydrogen gas discharge pipe connected to the cathode side storage tank to discharge the hydrogen gas from the cathode side storage tank, and a first valve provided in the hydrogen gas discharge pipe, the hydrogen gas is allowed to flow into the cathode side ejector from the hydrogen gas discharge line by circulating the cathode side circulation liquid from the cathode side storage tank to the cathode side ejector using the cathode side circulation pump, the cathode side fluid mixture feed pipe, and the cathode side circulation pipe, the hydrogen gas and the cathode side circulation liquid are mixed in the cathode side ejector, and an impurity in the hydrogen gas is transferred to the cathode side circulation liquid to remove the impurity from the hydrogen gas, and a pressure of the hydrogen gas stored in the cathode side storage tank is raised by controlling a flow rate of the cathode side circulation liquid circulated from the cathode side storage tank to the cathode side ejector and opening and closing of the first valve.