The present invention aims at providing a structure whereby, in the step of injecting a sample in a microquantity into a well, the migration of the sample into another well or overflow thereof can be prevented; and a structure whereby the position of the injected sample can be adjusted in a well or the sample can be transferred into the next well under controlling. It also aims at providing an apparatus for detecting chemotaxis of cells and separating chemotactic cells with the application of the above structures. Accordingly, the present invention provides a microsample treatment apparatus and an apparatus for detecting chemotaxis of cells and separating chemotactic cells wherein a plural number of wells are connected to each other via a part having resistance to fluids and the wells are each provided with tubes for injecting/sucking a sample and, if necessary, tubes for relieving pressure changes at the injection/suction, characterized in that these tubes have a space in common at the top ends thereof in which a liquid can be held.