An objective of the present invention is to provide: a cancer stem cell isolated using a cell marker; a substantively homogeneous cancer stem cell population including said cancer stem cell; and a method of preparing said cancer stem cell population. Another objective of the present invention is to provide: a method for separating cancer stem cells with a high proliferative potential and those with a low proliferative potential; a method for inducing cancer stem cells to have a different proliferative potential; and cancer stem cells separated or induced by these separation or induction methods. A further objective of the present invention is to provide: a method of screening for pharmaceuticals using said cancer stem cell or cancer stem cell population; a method for detecting the presence of said cancer stem cell or cancer stem cell population and for identifying or quantifying the same. The present inventors discovered that highly pure colon cancer stem cells (CSC) can be obtained in a large quantity, and identified two types of states of colon CSCs distinguishable through Lgr5 expression.