A method for manufacturing an ejection element substrate, which is provided with a flow-channel-forming member having an ejection orifice for ejecting a liquid and a liquid flow channel that is communicated with the ejection orifice, a substrate having a supply port for supplying the liquid to the liquid flow channel, and a filter structure formed in the bottom of the supply port, includes: forming the supply port by forming a through-hole by etching the substrate from a second face of the substrate on the side opposite to a first face of the substrate, on which the flow-channel-forming member is disposed; providing a resinous protection film on the side face and the bottom of the supply port; and forming a minute opening in the resinous protection film in the bottom of the supply port by carrying out a laser processing from the side of the second face.