An antenna-mounted substrate includes a first patch antenna, a second patch antenna disposed to face one principal surface of the first patch antenna, and a ground electrode disposed to face the other principal surface of the first patch antenna, the antenna-mounted substrate further including an antenna holding layer holding the second patch antenna, an inter-antenna layer positioned between the first patch antenna and the second patch antenna, and a substrate layer positioned between the first patch antenna and the ground electrode, those three layers being positioned in the mentioned order, wherein the inter-antenna layer is made of a dielectric material, and a relation of εr3>εr1≥εr2 is satisfied on an assumption that a relative permittivity of the antenna holding layer is denoted by εr1, a relative permittivity of the inter-antenna layer is denoted by εr2, and a relative permittivity of the substrate layer is denoted by εr3.