Patent ID: 8415071

Claim:
An electrolyte membrane, comprising: a membrane body comprising: a filler; and a polymer electrolyte, wherein a thickness of the membrane body is 1 micrometer to 500 micrometer, a moisture content of the membrane body is 10 mass % or more, and a swelling anisotropy of a swelling ratio in a membrane surface direction of the membrane body to a swelling ratio in a membrane thickness direction of the membrane body satisfies an equation having the form: λ ⁢ ⁢ xy λ ⁢ ⁢ z < 0.3 where Lambda z is the swelling ratio in the membrane thickness direction, and Lambda xy is the swelling ratio in the membrane surface direction, and wherein an angle made by a center axis in a longitudinal direction of the filler and a surface parallel to the membrane surface direction is within 45 degrees.