In a circuit module, even if a transmission signal output from a transmission electrode of a mounting substrate to a transmission terminal of a splitter leaks into a ground electrode, the transmission signal that has leaked into the ground electrode flows into via conductors that are connected along an edge portion of the ground electrode close to the transmission electrode and connected to a ground line of a motherboard. Therefore, the transmission signal that has been output from the transmission electrode and leaked into the ground electrode is prevented from traveling along an edge portion of the ground electrode toward a reception electrode side. Thus, characteristics of isolation between the transmission electrode and the reception electrode provided on the mounting substrate on which the splitter is mounted are improved.