A fluid on-off valve device comprising: a valve seat portion; a valve body (35, 40) contacting and separating from the valve seat portion to communicate and block between upstream and downstream paths in a fluid passage, wherein: the valve body (35, 40) includes a first seal portion sealing between the valve seat portion and the valve body (35, 40) and a second seal portion (37, 41) having higher hardness than the first seal portion; a direction in which the valve body (35, 40) contacts and separates from the valve seat portion and a flow direction of the fluid introduced from the upstream path in the fluid passage cross each other; the first seal portion includes a flange portion substantively extending horizontally inward from a lower edge of a cylindrical portion disposed in parallel to the valve seat portion; the second seal portion (37; 41) includes an end surface (37a, 41a) which faces and is disposed in parallel to the valve seat portion; in blocking the fluid passage by a differential pressure between upstream and downstream paths in the fluid passage, when the differential pressure is less than a predetermined value, the first seal portion is allowed to come into close contact with the valve seat portion for blocking of the fluid passage and, on the other hand, when the differential pressure is the predetermined value or higher, the first seal portion in close contact with the valve seat portion is allowed to be compressively deformed by the differential pressure and the second seal portion (37; 41) is allowed to come into close contact with the valve seat portion for blocking of the fluid passage; and a distance between the end surface of the first seal portion and the valve seat portion is set shorter than the distance between the end surface (37a, 41a) of the second seal portion (37, 41) and the valve seat portion, the fluid on-off valve device being characterized by: including restoring means giving a restoring force to the compressively-deformed first seal portion. the valve body (35, 40) includes a first seal portion sealing between the valve seat portion and the valve body (35, 40) and a second seal portion (37, 41) having higher hardness than the first seal portion; a direction in which the valve body (35, 40) contacts and separates from the valve seat portion and a flow direction of the fluid introduced from the upstream path in the fluid passage cross each other; the first seal portion includes a flange portion substantively extending horizontally inward from a lower edge of a cylindrical portion disposed in parallel to the valve seat portion; the second seal portion (37; 41) includes an end surface (37a, 41a) which faces and is disposed in parallel to the valve seat portion; in blocking the fluid passage by a differential pressure between upstream and downstream paths in the fluid passage, when the differential pressure is less than a predetermined value, the first seal portion is allowed to come into close contact with the valve seat portion for blocking of the fluid passage and, on the other hand, when the differential pressure is the predetermined value or higher, the first seal portion in close contact with the valve seat portion is allowed to be compressively deformed by the differential pressure and the second seal portion (37; 41) is allowed to come into close contact with the valve seat portion for blocking of the fluid passage; and a distance between the end surface of the first seal portion and the valve seat portion is set shorter than the distance between the end surface (37a, 41a) of the second seal portion (37, 41) and the valve seat portion, the fluid on-off valve device being characterized by: including restoring means giving a restoring force to the compressively-deformed first seal portion. including restoring means giving a restoring force to the compressively-deformed first seal portion.