Provided is a MEMS module that includes a MEMS element having a first capacitor electrode that can be displaced, a second capacitor electrode that opposes the first capacitor electrode, and driving electrodes that cause the first capacitor electrode to be displaced. The driving electrodes are connected to a control unit that applies a driving voltage to the driving electrodes and monitor terminals for detecting power. Thus, an element for monitoring power is not needed and a MEMS module, a variable reactance circuit and an antenna device are provided that are capable of realizing smaller size and lower loss.