A printed wiring board includes a first conductor layer including a first conductor circuit and a second conductor circuit formed adjacent to the first circuit, a resin insulating layer formed on the first conductor layer such that the insulating layer is filling space between the first and second conductor circuits, and a second conductor layer formed on the insulating layer such that distance (T) between the first and second conductor layers is in the range of 4.5 μm to 10.5 μm. The resin insulating layer includes inorganic particles having average particle diameter (D1) such that ratio (D1/S) of the diameter (D1) to distance (S) of the space is less than 0.25 and that ratio (D1/T) of the diameter (D1) to the distance (T) is less than 0.25, where the distance (S) of the space between the first and second conductor circuits is in the range of 4.5 μm to 10.5.