A deposition mask in which deformation of long sides is restrained is manufactured. A manufacturing method of a deposition mask includes a step of preparing a metal plate; a processing step of processing the metal plate into an intermediate product comprising: a plurality of deposition mask portions each including a pair of long sides and a pair of short sides, and having a plurality of through-holes formed therein; and a support portion that surrounds the plurality of deposition mask portions, and is partially connected to the short sides of the plurality of deposition mask portions; and a separation step of separating the deposition mask portions from the support portion to obtain the deposition mask. In the intermediate product, the long sides of the deposition mask portions are not connected to the support portion.