A fuel cell (20; 220; 420; 520; 620; 720; 820; 920; 1020; 1120; 1220; 1320; 1430) including a separator (50; 250; 550; 650; 1050; 1150; 1250; 1350; 1450) and a power generating body (45; 245; 445; 645; 745; 845; 945; 1345; 1445), the separator (50; 250; 550; 650; 1050; 1150; 1250; 1350; 1450) and power generating body (45; 245; 445; 645; 745; 845; 945; 1345; 1445) being laminated each other, and the power generating body (45; 245; 445; 645; 745; 845; 945; 1345; 1445) being equipped at least with an electrolyte membrane (30; 230; 430; 630; 730; 830; 930; 1330; 1430), anode and cathode, comprising: a sealing part that seals reaction gas supplied for electrochemical reactions at the fuel cell (20; 220; 420; 520; 620; 720; 820; 920; 1020; 1120; 1220; 1320; 1430) between the power generating body (45; 245; 445; 645; 745; 845; 945; 1345; 1445) and the separator (50; 250; 550; 650; 1050; 1150; 1250; 1350; 1450) at an outer circumference part of the fuel cell (20; 220; 420; 520; 620; 720; 820; 920; 1020; 1120; 1220; 1320; 1430), wherein a convex part (32; 232; 432; 632; 732; 832; 932; 1032; 1132; 1232; 1332; 1456) and a recess (52; 252; 552; 652; 1052; 1152; 1252; 1352; 1437) are fit together in the sealing part, the convex part (32; 232; 432; 632; 732; 832; 932; 1032; 1132; 1232; 1332; 1456) being formed projecting in the lamination direction on one of the power generating body (45; 245; 445; 645; 745; 845; 945; 1345; 1445) and the separator (50; 250; 550; 650; 1050; 1150; 1250; 1350; 1450), and at least one of the convex part (32; 232; 432; 632; 732; 832; 932; 1032; 1132; 1232; 1332; 1456) and the recess (52; 252; 552; 652; 1052; 1152; 1252; 1352; 1437) is formed with a polymer material that expands with moisture absorption, characterized in that the recess (52; 252; 552; 652; 1052; 1152; 1252; 1352; 1437) is formed recessed in the lamination direction on the other of the power generating body (45; 245; 445; 645; 745; 845; 945; 1345; 1445) and the separator (50; 250; 550; 650; 1050; 1150; 1250; 1350; 1450), and the fuel cell (20; 220; 420; 520; 620; 720; 820; 920; 1020; 1120; 1220; 1320; 1430) has a gap between a projecting tip of the convex part (32; 232; 432; 632; 732; 832; 932; 1032; 1132; 1232; 1332; 1456) and a recessed bottom surface of the recess (52; 252; 552; 652; 1052; 1152; 1252; 1352; 1437) in a state for which the at least one of the convex part (32; 232; 432; 632; 732; 832; 932; 1032; 1132; 1232; 1332; 1456) and the recess (52; 252; 552; 652; 1052; 1152; 1252; 1352; 1437) formed using the polymer material has expanded due to moisture absorption. a sealing part that seals reaction gas supplied for electrochemical reactions at the fuel cell (20; 220; 420; 520; 620; 720; 820; 920; 1020; 1120; 1220; 1320; 1430) between the power generating body (45; 245; 445; 645; 745; 845; 945; 1345; 1445) and the separator (50; 250; 550; 650; 1050; 1150; 1250; 1350; 1450) at an outer circumference part of the fuel cell (20; 220; 420; 520; 620; 720; 820; 920; 1020; 1120; 1220; 1320; 1430), wherein a convex part (32; 232; 432; 632; 732; 832; 932; 1032; 1132; 1232; 1332; 1456) and a recess (52; 252; 552; 652; 1052; 1152; 1252; 1352; 1437) are fit together in the sealing part, the convex part (32; 232; 432; 632; 732; 832; 932; 1032; 1132; 1232; 1332; 1456) being formed projecting in the lamination direction on one of the power generating body (45; 245; 445; 645; 745; 845; 945; 1345; 1445) and the separator (50; 250; 550; 650; 1050; 1150; 1250; 1350; 1450), and at least one of the convex part (32; 232; 432; 632; 732; 832; 932; 1032; 1132; 1232; 1332; 1456) and the recess (52; 252; 552; 652; 1052; 1152; 1252; 1352; 1437) is formed with a polymer material that expands with moisture absorption, characterized in that the recess (52; 252; 552; 652; 1052; 1152; 1252; 1352; 1437) is formed recessed in the lamination direction on the other of the power generating body (45; 245; 445; 645; 745; 845; 945; 1345; 1445) and the separator (50; 250; 550; 650; 1050; 1150; 1250; 1350; 1450), and the fuel cell (20; 220; 420; 520; 620; 720; 820; 920; 1020; 1120; 1220; 1320; 1430) has a gap between a projecting tip of the convex part (32; 232; 432; 632; 732; 832; 932; 1032; 1132; 1232; 1332; 1456) and a recessed bottom surface of the recess (52; 252; 552; 652; 1052; 1152; 1252; 1352; 1437) in a state for which the at least one of the convex part (32; 232; 432; 632; 732; 832; 932; 1032; 1132; 1232; 1332; 1456) and the recess (52; 252; 552; 652; 1052; 1152; 1252; 1352; 1437) formed using the polymer material has expanded due to moisture absorption.