A cell processing apparatus 29 of the present invention includes a storage container 57 that can contain liquid L including a biological sample; a filter 60 that prevents a first cell C1 in the biological sample from passing therethrough and that allows a second cell C2 having a smaller diameter than that of the first cell C1 to pass therethrough; and a filtration cylinder 58 for separating, in the storage container 57 and via the filter 60, the liquid L into a first liquid L1 mainly including the first cell C1 and a second liquid L2 mainly including the second cell C2. A measurement target cell discriminated by the filter from the other cells can be easily collected.