A liquid ejection head substrate has heating unit and an element array in which a plurality of ejection energy generating elements generating ejection energy for liquid ejection are arranged on a surface side of a base material. The heating unit includes a heating element extending in a direction of the element array and generating heat by being energized, wiring spaced apart from the heating element in a direction orthogonal to the surface of the base material, and a plurality of connecting portions connecting the heating element and the wiring to each other. The heating element, the wiring, and the plurality of connecting portions are provided in a region overlapping a region where the element array is disposed in a direction orthogonal to the direction of the element array when seen from the direction orthogonal to the surface of the base material. A current flows to the wiring in a middle of a path of the current flowing through the heating element when the heating element is energized.