Provided is a chip or the like having a particulate concentrating mechanism such as a mechanism that can selectively concentrate nucleated red blood cells contained in maternal blood and derived from a fetus and can collect the concentrated liquid rich in nucleated red blood cells, and also provided is a nucleated red blood cell concentrating/collecting method. A micro-channel chip for concentrating nucleated red blood cells has an inlet-side channel, an outlet-side channel, and a separation narrow channel provided between the inlet-side channel and the outlet-side channel. The separation narrow channel has an inner wall having a dimension through which non-nucleated red blood cells easily pass and nucleated red blood cells hardly pass, and has a means for deforming or moving part of the inner wall of the channel to have a dimension through which nucleated red blood cells easily pass. The following are also provided: a method for collecting a liquid in which nucleated red blood cells obtained by using this chip are concentrated; and a micro-channel chip for concentrating particulates other than for concentrating nucleated red blood cells.
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