A membrane electrode assembly includes a rod-shaped or tubular anode, an anode terminal connected to the anode, a cathode disposed at a position apart from the anode so as to face the anode, and a membrane that separates the anode from the cathode. The cathode includes a line-shaped or strip-shaped cathode-supporting portion and a cathode claw that extends to the left, right, or both left and right from the cathode-supporting portion and that is curved along an outer periphery of the anode. The cathode-supporting portion and the cathode claw form an anode-holding portion of the cathode. The membrane includes a membrane strip, and the membrane strip is disposed on the cathode claw to be in contact with the cathode claw so that the anode is held by the anode-holding portion of the cathode with the membrane strip therebetween.