A multilayer circuit substrate has a high frequency switch embedded therein. In the multilayer circuit substrate, a first conductive layer that faces a main surface of the high frequency switch through an insulating layer has circuit patterns formed therein so as to be connected to input/output terminals through via conductors. The first conductive layer has an opening pattern in which a ground conductor is not present in a region that faces the main surface of the high frequency switch and that is outside of the circuit patterns. In a third conductive layer disposed outer side of the first conductive layer with respect to the high frequency switch, a ground conductor is formed at least in a region where the main surface of the high frequency switch is projected in the thickness direction.