A controller and method changing a frequency of a control (or carrier) signal in accordance with a waveform that periodically changes within a first frequency range from a frequency fc1 to a frequency fc2, where the frequency fc1 is smaller than the frequency fc2, and a second frequency range from a frequency fc3 to a frequency fc4, where the frequency fc3 is smaller than the frequency fc4. The frequencies fc1 and fc4 satisfy the inequalities (n−1)·fc4≦n·fc2 and n·fc3≦(n+1)·fc1 and/or satisfy an approximate expression n·fc4≈(n+1)·fc1 where n is an integer. The frequencies fc2 and fc3 satisfy the inequalities n·fc2≦fs−Δfs and fs+Δfs≦n·fc3 where fs±Δfs represents a predetermined frequency band.