A chip comprising a micro-channel unit for hydraulically classifying cells in a blood sample, wherein the micro-channel unit comprises a pattern in which a main channel through which the blood sample flows, a sub channel connected to a side of the main channel, a removal channel connected, downstream from the sub channel, to a side of the main channel opposite to the side thereof to which the sub channel is connected, and a collection channel connected, downstream from the removal channel, to the side of the main channel opposite to the side thereof to which the sub channel is connected are two-dimensionally extended, liquid flowing from the sub channel into the main channel pushes cells flowing in the main channel toward the side thereof on which the removal channel and the collection channel are disposed, fluid containing non-nucleated RBCs among the pushed cells enters the removal channel, so that the non-nucleated RBCs are removed from the blood sample, fluid containing target cells among the remaining cells from which the non-nucleated RBCs have been removed enters the collection channel, so that the target cells are acquired from the blood sample, a volume of flow per unit time, in each collection channel, on a cross section of a connecting part between the main channel and that collection channel is larger than a volume of flow per unit time, in each removal channel, on a cross section of a connecting part between the main channel and that removal channel, a plurality of micro-channel units having the same patterns as each other are repeatedly stacked in a height direction, and inlets of the main channels, inlets of the sub channels, outlets of the removal channels, outlets of the collection channels, and outlets of the main channels, which are provided in the micro-channel units, are connected to respective pillar channels penetrating each layer in a traversing manner so that they are separately put together by the respective pillar channels. the micro-channel unit comprises a pattern in which a main channel through which the blood sample flows, a sub channel connected to a side of the main channel, a removal channel connected, downstream from the sub channel, to a side of the main channel opposite to the side thereof to which the sub channel is connected, and a collection channel connected, downstream from the removal channel, to the side of the main channel opposite to the side thereof to which the sub channel is connected are two-dimensionally extended, liquid flowing from the sub channel into the main channel pushes cells flowing in the main channel toward the side thereof on which the removal channel and the collection channel are disposed, fluid containing non-nucleated RBCs among the pushed cells enters the removal channel, so that the non-nucleated RBCs are removed from the blood sample, fluid containing target cells among the remaining cells from which the non-nucleated RBCs have been removed enters the collection channel, so that the target cells are acquired from the blood sample, a volume of flow per unit time, in each collection channel, on a cross section of a connecting part between the main channel and that collection channel is larger than a volume of flow per unit time, in each removal channel, on a cross section of a connecting part between the main channel and that removal channel, a plurality of micro-channel units having the same patterns as each other are repeatedly stacked in a height direction, and inlets of the main channels, inlets of the sub channels, outlets of the removal channels, outlets of the collection channels, and outlets of the main channels, which are provided in the micro-channel units, are connected to respective pillar channels penetrating each layer in a traversing manner so that they are separately put together by the respective pillar channels.