In order to implement an MEMS device which monitors a mechanical response characteristic of a moving part to detect a precursor of a fatal failure without needing correction of an existing control input and without adding any components, there are provided vibration detecting means 80 for detecting a micro vibration excited in a moving part 60 in one of binary switching states, a dynamic-characteristic analyzing unit which analyzes a dynamic characteristic of the moving part 60 on the basis of an output from the detection, a memory 100 which stores the analyzed data, an operation unit 110 which retrieves the stored data, compares two temporally successive pieces of data and calculates difference information between the two pieces of data, and a failure diagnosis unit 120 which performs failure diagnosis based on the difference information.