Abstract: A high pressure tank has a cylindrical liner and a fiber reinforced plastic layer which covers the outer surface of the liner. At least one end of the liner is separable. The liner includes a cylindrical liner body and a lid. An O-ring is located between the contact surfaces of the liner body and the lid in the circumferential direction. Each contact surface has a seal surface which contacts the O-ring. One of the liner body and the lid has a deformable portion which deforms toward the seal surfaces. The structure can securely seal the separated portions of the liner when the high pressure tank is in a high pressure state.