Abstract: A circuit board and an electronic device having the circuit board that includes a ceramic sintered body, a through conductor and a metal wiring layer. The ceramic sintered body includes a through hole penetrating from a first main surface to a second main surface thereof. The through conductor is in the through hole and has first and second ends. The metal wiring layer covering the first end and electrically connected to the through conductor. The through conductor includes: a first portion having a hollow cylinder shape, in contact with an inner wall of the through hole and extending from the first end to the second end; and a second portion having a columnar shape and disposed inside the first portion. The second portion has an average grain size of the metal larger than that in the first portion.