Provided is a LYPD1 inhibitor for promoting vascular endothelial network formation in a biological tissue. Also provided is a medicinal composition, said medicinal composition comprising a LYPD1 inhibitor as an active ingredient, for treating and/or preventing neoangiogenic disorders. Also provided is a method which comprises: (a1) a step for providing a cell population containing first cells expressing LYPD1 and vascular endothelial cells； (a2) a step for treating the cell population obtained in step (a1) with a LYPD1 inhibitor； and (a3) a step for culturing the cell population obtained in step (a2).
