A recording element substrate includes a substrate; an insulating layer disposed on the substrate; a plurality of heating portions which are arranged on the insulating layer and which produce thermal energy used to eject a liquid; and a plurality of heat conduction members, each being located between adjacent heating portions with respect to an arrangement direction of the heating portions, the heat conduction members being located between the substrate side principal surface of the insulating layer and the heating portion side principal surface of the insulating layer and having higher thermal conductivity than the insulating layer. The heat conduction members are in contact with a heat conduction layer which has higher thermal conductivity than the insulating layer.