A method of manufacturing a liquid ejection head includes the steps of (1) forming a recess in a second surface of a substrate to form a common supply port, (2) forming an etching mask, which specifies opening positions of independent supply ports, on a bottom surface of the common supply port, and (3) performing ion etching using plasma with the etching mask employed as a mask, thereby forming the independent supply ports. The etching mask has an opening pattern formed therein such that respective distances from an ejection energy generation element to openings of two independent supply ports adjacent to the ejection energy generation element on the first surface side of the substrate are equal to each other.