A cycle setting unit of a signal generating circuit varies a set cycle value. A first determining unit determines a first ON time on the basis of: a first duty ratio obtained by correcting, with a correction value, a ratio between a target ON time and a reference cycle; and a set cycle value. A second determining unit determines, as a second ON time, a setting candidate value that is close to the first ON time. A generating unit generates a PWM signal reflecting the set cycle value and the second ON time. A third determining unit determines the correction value that is to be used next time by the first determining unit, on the basis of the target ON time, the reference cycle, the correction value of the previous time, the set cycle value, and the second ON time.