To provide a complex circuit board having a high-frequency transmission channel connection structure that surely transfers high-frequency signals between two boards and prevents transmission loss in the high-frequency signals.

In this complex circuit board, a thickness from the top in the first circuit board A to an inner layer ground conductor 4 is equal to a thickness of the second dielectric substrate 11, a notch 1c is formed from the top to the inner layer ground conductor 4 at both sides of the first channel conductor 2 at the side of the first circuit board A, a projection 11c is formed at both sides of the second channel conductor 12 at the side of the second circuit board B, the second ground conductor 13 at the same side and the lower ground conductor 14 are extended at the upper and lower sides, the projection 11c is fitted and adhered to the notch 1c with wax materials.