A composite member having an excellent heat resistance is provided. The composite member includes: a substrate composed of a composite material including a non-metal phase and a metal phase; and a metal layer that covers at least a portion of a surface of the substrate, wherein a metal included in each of the metal phase and the metal layer is mainly composed of Ag, and a ratio of a content of Cu to a total content of Ag and Cu in a boundary region of the metal layer with the substrate is less than or equal to 20 atomic %.