An electrolyzer comprising an electrolyzer gasket incorporated in the electrolyzer, comprising: an anode ; a cathode ; and a sheet-like separator that isolates the anode and the cathode , the electrolyzer gasket being for holding the separator , wherein the electrolyzer has: a picture-frame-shaped anode metal frame having an opening for forming an anode chamber in a central part; and a cathode metal frame having the same shape as the anode metal frame and having an opening for forming a cathode chamber in a central part, the anode is attached at the opening of the anode metal frame , the cathode is attached at the opening of the cathode metal frame , and the electrolyzer gasket is sandwiched in a tight state between the anode metal frame and the cathode metal frame , the electrolyzer gasket comprises a single picture-frame-shaped thin-plate-like frame having approximately the same shape as the anode metal frame and the cathode metal frame , the picture-frame-shaped thin-plate-like frame has: a first surface being in close contact with the anode metal frame ; and a second surface being in close contact with the cathode metal frame , and has a structure obtained by forming, on any one of the first surface and the second surface , a notch having a difference in level of approximately the same thickness as the thickness of the separator , the notch formed by thinly scraping off, in a uniform thickness, a region including an edge on the anode or the cathode of the thin-plate-like frame, and an edge part of the separator is accommodated in a gap formed between the notch and the anode metal frame or the cathode metal frame , and the separator is held in a state of being nearer to the surface of the anode or the surface of the cathode. the electrolyzer has: a picture-frame-shaped anode metal frame having an opening for forming an anode chamber in a central part; and a cathode metal frame having the same shape as the anode metal frame and having an opening for forming a cathode chamber in a central part, the anode is attached at the opening of the anode metal frame , the cathode is attached at the opening of the cathode metal frame , and the electrolyzer gasket is sandwiched in a tight state between the anode metal frame and the cathode metal frame , the electrolyzer gasket comprises a single picture-frame-shaped thin-plate-like frame having approximately the same shape as the anode metal frame and the cathode metal frame , the picture-frame-shaped thin-plate-like frame has: a first surface being in close contact with the anode metal frame ; and a second surface being in close contact with the cathode metal frame , and has a structure obtained by forming, on any one of the first surface and the second surface , a notch having a difference in level of approximately the same thickness as the thickness of the separator , the notch formed by thinly scraping off, in a uniform thickness, a region including an edge on the anode or the cathode of the thin-plate-like frame, and an edge part of the separator is accommodated in a gap formed between the notch and the anode metal frame or the cathode metal frame , and the separator is held in a state of being nearer to the surface of the anode or the surface of the cathode. <EOS>