A first vibration sensor measures vibration of a bearing. A second vibration sensor for measuring background noise received by the first vibration sensor is installed so as not to receive vibration of the bearing. A data acquisition device receives a first signal that is a measurement signal of the first vibration sensor and a second signal that is a measurement signal of the second vibration sensor and outputs a third signal obtained by subtracting the second signal from the first signal as data indicating vibration of the bearing.