To provide a manufacturing method of a metal mask which keeps the smoothness of the inner wall of an opening part enhanced and thereby stabilizes the quantity of application of a solder paste.

The opening part of a pattern for printing is formed in a metal plate 10 by exposure to a laser light. An abrasive solution containing minute abrasive grains is encapsulated in the opening part and the inner wall of the opening part is polished by applying vibration to the metal plate 10. Then, an abrasive material consisting of the abrasive solution 30 and extremely thin fibers 50 is brought into contact with the inner wall 12 of the opening part to polish the inner wall 12. The abrasive solution 30 is a mixture of a nitrate containing minute abrasive grains 31 of alumina and water.