To provide a transmission module in which increase in the insertion loss of a core isolator element is minimized.

A circuit board 2 is a multilayer board including ground patterns 3A-3D. A power amplifier 10 and a core isolator element 14 are mounted on the circuit board 2. The power amplifier 10 and the core isolator element 14 are covered with a resin layer 12. A shield layer 13 is provided on the surface of the resin layer 12. Increase in the insertion loss due to the core isolator element 14 is minimized by separating the interval between the top surface 14A of the core isolator element 14 and the top surface shield layer 13A of the shield layer 13 facing the top surface 14A, and the interval between the side surface of the core isolator element 14 and the side surface shield layer of the shield layer 13 facing the side surface by a predetermined distance.