In a high-frequency switch module, a switch IC is mounted on a multilayer board to define a high-frequency switch module. The multilayer board includes two internal wirings and two internal ground electrodes. The internal ground electrodes are spaced apart from each other at an interval when viewed from a lamination direction of the multilayer board. The first internal wiring is located on the upper surface side of the first internal ground electrode, and is entirely separated from an RF wiring, and the first internal wiring includes a power supply wiring for supplying power to the switch IC. The second internal wiring is located on the upper surface side of the second internal ground electrode, and is entirely separated from the power supply wiring, and the second internal wiring includes a signal wiring through which an RF signal propagates.