In order to provide a novel nitric oxide generation regulator for effectively regulating nitric oxide generation from vascular endothelial cells, macrophage cells including microglial cells, and the like that can be safely used in vivo, disclosed is a nitric oxide generation regulator that has the trinuclear pentamethine cyanine dye represented by the belowmentioned general formula (1) as the active ingredient. (In the general formula (1), R represents a potentially branched alkyl group having 2-4 carbon atoms, and X- represents an appropriate counteranion.)
