The invention provides a highly-reliable circuit board and an electronic device obtained by mounting electronic components on the circuit board, which have high bonding strength and excellent heat discharge properties, and can be used over a long period as a result of minimizing cavities in a metal wiring layer formed on a through conductor. A circuit board (10) is provided with a through conductor (13) comprising a metal in a through hole (12) that penetrates in the thickness direction of a ceramic sintered body (11), and a metal wiring layer (14) that covers and is connected to the surface of the through conductor (13) on at least one main surface side of the ceramic sintered body (11). The through conductor (13) comprises: a first area (13a) that is positioned on an inner wall side of the through hole (12), from one end to the other end of the through hole (12) in the thickness direction of the ceramic sintered body (11); and a second area (13b) that adjoins the first area (13a). The average crystal grain size in the second area (13b) is larger than the average crystal grain size in the first area (13a).