An object of an embodiment of the present invention is to provide a method with which it is possible to easily distinguish a proliferation phase of a cell cycle from a resting phase thereof in real time. The object of the embodiment of the present invention is attained by providing a method for performing phase identification of the cell cycle, the method including: visualizing one or more gene-expression products as markers whose amounts in a cell change in a cell-cycle dependent manner; and detecting the products so as to distinguish the proliferation phase of the cell cycle from the resting phase thereof.