A flow passage partition structure including a flow passage member including a flow passage space portion, a partition member partitioning the flow passage space portion into a first flow passage and a second flow passage, the partition member including a first plate and a second plate being in contact with the first plate in a state where the second plate is press-fitted in an inner circumferential surface of the flow passage space portion, the first plate including an outer circumferential surface that is out of contact with the inner circumferential surface of the flow passage space portion, and the first plate, the second plate, and the inner circumferential surface of the flow passage space portion forming a space portion that corresponds to a foreign material storage portion.