According to one embodiment, an exciter comprises a sine wave generator, a filter, a digital/analog converter, and a quadrature modulator. The sine wave generator generates a first sine wave and a second sine wave while changing a frequency in a predetermined step at a preset time interval. The filter sets one of stored filter coefficients and performs filter processing for the first sine wave and the second sine wave. The digital/analog converter converts the first sine wave and the second sine wave after the filter processing into a first analog signal and a second analog signal, respectively. The quadrature modulator quadrature-modulates the first analog signal and the second analog signal.