Substrate for high-frequency printed wiring board

A substrate for a high-frequency printed wiring board, the substrate comprising:

• a dielectric layer including a fluororesin and an inorganic filler;
• and
• a copper foil layered on at least one surface of the dielectric layer, wherein
• a surface of the copper foil at the dielectric layer side has a maximum height roughness (Rz) of less than or equal to 2 μm, and
• in a cross section of the dielectric layer in a direction perpendicular to the copper foil, a ratio of a total cross sectional area of the inorganic filler to an overall cross sectional area in a region at a distance of more than or equal to 18 0 μm and less than or equal to 22 2μm from the copper foil is 0.7 time or less as large as a ratio of a total cross sectional area of the inorganic filler to an overall cross sectional area in a region at a distance of more than or equal to 0 18 μm and less than or equal to 2 22 μm from the copper foil.