The present invention provides a method of forming a micro metal bump, which is capable of stably and industrially forming a micro metal bump, by a gas deposition process, at a prescribed position of a metal part formed on one side surface of a substrate. The method comprises the steps of: forming a straight hole (34) in a mask layer (30) covering one side surface of a substrate (10) on which a wiring pattern (12) is formed, wherein a prescribed position of the wiring pattern (12) is exposed in a bottom surface of the straight hole and the straight hole has an inner wall perpendicular to the one side surface of the substrate (10) and a sharp top opening portion; providing a metal plate, whose area is larger than that of the substrate (10), on the other side surface of the substrate (10) as a heat sink; placing the substrate (10) and the metal plate in a vacuum; forming a tapered metal bump (14) on the exposed surface of the wiring pattern (12), which is exposed in the bottom surface of the straight hole (34), by a gas deposition process, in which metal nanoparticles obtained by evaporating a metal are ejected from a nozzle together with a carrier gas so as to deposit on the prescribed position, with cooling the substrate (10) to a temperature lower than upper temperature limit of resin constituting the mask layer (30), by the metal plate as the heat sink, so as to retain a configuration of the straight hole (34); and removing the mask layer (30) from the one side surface of the substrate so as to complete the tapered metal bump (14) at the prescribed position of the wiring pattern (12).