To provide a technology of staining nuclei of cells, microorganisms and the like by a simple operation and observing their forms.There is provided a cell nucleus observation substrate including an introduction part into which a sample liquid containing cells is introduced and an observation area within which the cells in the sample liquid introduced from the introduction part is held, copper being disposed on a flow path of the sample liquid in the introduction part and the observation area so that the copper being capable of contacting with the sample liquid. In the cell nucleus observation substrate, the cells in the sample liquid introduced from the introduction part is contacted with copper, nucleic acids therein will emit fluorescence and is held within the observation area. Accordingly, in the cell nucleus observation substrate, the cells including the nuclei being fluorescence stained can be observed at the observation area.