A yarn cooler comprising: a yarn cooling unit configured to cool a yarn spun out from a spinning apparatus, by applying gas to the yarn; and a duct in which a passage where the gas supplied to the yarn cooling unit flows is formed, the duct including: a passage-enlarged portion including an inner wall surface which is formed to increase the width of the passage from an upstream side toward a downstream side of the passage; and partition plates which are lined up in a passage width direction and are radially provided from the upstream side toward the downstream side, in the passage-enlarged portion, bulging portions being formed at end portions on the upstream side of the respective partition plates, each of the bulging portions including a part which increases in size in the passage width direction from the end portion on the upstream side of the bulging portion toward the downstream side, and the length of the gap between two bulging portions of neighboring two of the partition plates being 12mm or longer and 30mm or shorter, wherein, in a passage length direction which is orthogonal to the passage width direction, the length of each of the partition plates is at least 26% of the length of the inner wall surface. a yarn cooling unit configured to cool a yarn spun out from a spinning apparatus, by applying gas to the yarn; and a duct in which a passage where the gas supplied to the yarn cooling unit flows is formed, the duct including: a passage-enlarged portion including an inner wall surface which is formed to increase the width of the passage from an upstream side toward a downstream side of the passage; and partition plates which are lined up in a passage width direction and are radially provided from the upstream side toward the downstream side, in the passage-enlarged portion, bulging portions being formed at end portions on the upstream side of the respective partition plates, each of the bulging portions including a part which increases in size in the passage width direction from the end portion on the upstream side of the bulging portion toward the downstream side, and the length of the gap between two bulging portions of neighboring two of the partition plates being 12mm or longer and 30mm or shorter, wherein, in a passage length direction which is orthogonal to the passage width direction, the length of each of the partition plates is at least 26% of the length of the inner wall surface. a passage-enlarged portion including an inner wall surface which is formed to increase the width of the passage from an upstream side toward a downstream side of the passage; and partition plates which are lined up in a passage width direction and are radially provided from the upstream side toward the downstream side, in the passage-enlarged portion, bulging portions being formed at end portions on the upstream side of the respective partition plates, each of the bulging portions including a part which increases in size in the passage width direction from the end portion on the upstream side of the bulging portion toward the downstream side, and the length of the gap between two bulging portions of neighboring two of the partition plates being 12mm or longer and 30mm or shorter,